The last 16 of the BNP Paribas Open has taken shape, with a host of barn-burners among the eight matches all scheduled for Tuesday's action.
The fourth round includes one former champion at the tournament, Victoria Azarenka (winner in 2012 and 2016) and one former finalist, 2019 runner-up Angelique Kerber.
Five Grand Slam winners are still in the draw, including reigning Roland Garros champion Barbora Krejcikova as well as Kerber, Azarenka, Jelena Ostapenko and Iga Swiatek.
Nine 2021 titlists have a chance to add to their season tally: Krejcikova, Kerber, Ostapenko, Swiatek, Anett Kontaveit, Ons Jabeur, Paula Badosa, Elina Svitolina and Leylah Fernandez.
Five of the six inhabited continents - all except Asia - are represented in the last 16, with Beatriz Haddad Maia delivering a tournament-best performance by a Brazilian in reaching this stage. Two home players remain, No.19 seed Jessica Pegula and Shelby Rogers. Belarus is the only other country with multiple representatives left, Azarenka and Aliaksandra Sasnovich - who square off against each other next.
The youngest player left in the draw is 18-year-old Fernandez, while the oldest is 33-year-old Kerber. The lowest-ranked is qualifier Anna Kalinskaya, the World No.151, followed by No.115-ranked lucky loser Haddad Maia.
Sweet 16— BNP Paribas Open (@BNPPARIBASOPEN) October 12, 2021
🇧🇷 Haddad Maia v. Kontaveit 🇪🇪
🇹🇳 Jabeur v. Kalinskaya 🇷🇺
🇪🇸 Badosa v. Krejcikova 🇨🇿
🇩🇪 Kerber v. Tomljanovic 🇦🇺
🇧🇾 Azarenka v. Sasnovich 🇧🇾
🇺🇸 Pegula v. Svitolina 🇺🇦
🇺🇸 Rogers v. Fernandez 🇨🇦
🇱🇻 Ostapenko v. Swiatek 🇵🇱#BNPPO21
[LL] Beatriz Haddad Maia (BRA) vs.  Anett Kontaveit (EST)
Reaching the Eastbourne final in June was a fine result for Kontaveit, but the Estonian has said that after losing it to Jelena Ostapenko, she hit "a low." It had been her eighth career final, but she had converted only one of those into a title - four years previously at 's-Hertogenbosch 2017.
Kontaveit went back to the drawing board and hired a new coach - Dmitry Tursunov, previously renowned for transforming Aryna Sabalenka from a one-note big hitter into a disciplined and well-rounded top tenner. Since August, a similar evolution has been evident in Kontaveit's game - but also an ability to relax and play her best tennis in important matches.
The 25-year-old has reached two finals in her past five tournaments, in Cleveland and Ostrava, and won both. She has won 15 of her past 16 matches and dethroned defending champion Bianca Andreescu to reach the fourth round of Indian Wells for the second time running.
The World No.115 Haddad Maia's upset of No.1 seed Karolina Pliskova delivered a host of noteworthy statistics. The 25-year-old became the first Brazilian to defeat a Top 3 player in the Open Era and the first lucky loser to reach the last 16 of Indian Wells since Rachel McQuillan in 2001. She also became the third-lowest ranked player to beat a Top 10 player this year (after the unranked Olivia Gadecki, who upset Sofia Kenin at the Phillip Island Trophy, and No.292 Anastasia Gasanova, who defeated Pliskova in Abu Dhabi).
But Haddad Maia has been threatening a result like this all year. The former World No.58 has compiled a 93-21 record at all levels since returning to the sport in September 2020, including nine ITF titles. The upset against Pliskova was her second Top 5 win. She previously defeated Sloane Stephens at Acapulco 2019.
Head-to-head: 0-0 at pro level, though Kontaveit won their only junior meeting 4-6, 6-3, 6-1 in the first round of Wimbledon 2012 and went on to reach the semifinals.
 Ons Jabeur (TUN) vs. [Q] Anna Kalinskaya (RUS)
Currently perched at No.9 in the Porsche Race to the WTA Finals, Jabeur has made no secret of her determination to seal a place in Guadalajara this year. The Tunisian's motivation has been demonstrated in an impeccable run of the consistency that used to elude her. She has now won multiple matches in 15 of her 18 tournaments this year.
There's also increasing discipline and efficiency, illustrated as Jabeur used the fiendishly windy conditions to her advantage to dispatch Danielle Collins for the loss of just four games in the third round. She will be bidding to reach her seventh quarterfinal of 2021 against surprise package Kalinskaya.
The Russian qualifier has historically posted her best results on U.S. hard courts. Her sole WTA semifinal to date came at Washington 2019, and her third-round run in Miami this March is the only other time this year that she has won back-to-back WTA main-draw matches.
World No.151 Kalinskaya, who reached a career high of No.96 in October 2019, has reached the fourth round the hard way. She has gone to three sets in each of her main-draw wins, over Claire Liu, No.28 seed Sara Sorribes Tormo and Viktorija Golubic. Against Liu and Golubic, Kalinskaya reversed losses to both players earlier this year.
 Barbora Krejcikova (CZE) vs.  Paula Badosa (ESP)
Krejcikova's Roland Garros title run came out of leftfield, but the Czech has been playing with the authority of a Grand Slam champion ever since. In the third round, she allowed neither a two-hour rain delay nor a talented young opponent hungry for a resurgence faze her and swatted Amanda Anisimova away in just 70 minutes.
Krejcikova, who is making her main-draw debut at Indian Wells, has now won 31 of her past 35 matches dating back to May, with her only losses coming to Ashleigh Barty, Aryna Sabalenka and Belinda Bencic - none of whom started in the BNP Paribas Open field. But she next faces the player who defeated her two tournaments prior to that hot streak beginning.
Badosa made a significant breakthrough in the first half 2021, compiling a 29-11 record through the Olympic Games. During that spell, the Spaniard was quick to credit coach Javier Marti, the former ATP player with whom she started working in 2020. The pair split after the Olympics, and Badosa would lose in the second round of three of her next four tournaments.
But the 23-year-old is proving she can continue her rise without Marti. A pair of quality wins over Dayana Yastremska and Coco Gauff have seen her into the Indian Wells fourth round on her main draw debut.
Head-to-head: 1-0 to Badosa, whose 6-1, 7-5 first-round defeat of Krejcikova in Madrid this year kickstarted a breakthrough run to her first WTA 1000 semifinal on home soil.
 Angelique Kerber (GER) vs. Ajla Tomljanovic (AUS)
The Kerber renaissance over the past five months hasn't just benefited her own results. When Kerber is at her best, tennis wins. Any given list of the best matches over the past decade would involve her name disproportionately. This week alone, she has added another two crowd-thrilling three-set victories over Katerina Siniakova and Daria Kasatkina.
One of the oddities of Kerber's career accomplishments is that the 33-year-old has yet to win a WTA 1000 trophy. Given that her 13 career titles include three Grand Slams, it's a mere curiosity rather than especially meaningful, but the 2019 runner-up will surely be motivated to go one step further this year.
Few players are as eloquent and self-aware about the psychological aspect of their results as Tomljanovic.
"I will overthink even the smallest things, which sometimes works for me and other times it doesn't," the Australian said after defeating Garbiñe Muguruza in the second round, just her fourth career Top 10 win. "Sometimes it's hard to accept the losses and it's hard to accept that maybe where I thought I'd be, I didn't hit those marks. It kind of builds in my mind that I kind of failed. Then I want it even more."
Tomljanovic has been exorcising some of those demons this year. A quarterfinal run at Wimbledon was a significant step; and now, 14 years after making her WTA main draw debut at Indian Wells 2009 as a 15-year-old wildcard, she is in the last 16 for the first time.
Head-to-head: 2-0 to Kerber, both matches - at Roland Garros 2015 and the US Open 2020 - won in straight sets.
 Victoria Azarenka (BLR) vs. Aliaksandra Sasnovich (BLR)
Is there a player who fits the "upset artist" tag better than Sasnovich right now? The 27-year-old owns six career Top 10 wins, a total that doesn't even include her consecutive straight-sets victories over Slam champions this week - No.17 seed Emma Raducanu followed by No.11 Simona Halep. When her neat, aggressive game is clicking, it's easy to see why she's a threat.
Yet Sasnovich has never been ranked higher than No.30 (in September 2018) and has spent more time floating around her current No.100 placement. She is yet to win a WTA title and has reached only two finals to date (Seoul 2015 and Brisbane 2018). This week marks the first time she has won three straight WTA main draw matches since Sydney 2019.
"It's interesting to play against the players who are the best in the world," Sasnovich said after defeating Raducanu. "I prefer to play on the big arena with a lot of crowds."
She'll get a shot at another upset against a Belarusian compatriot next. Azarenka owns the best Indian Wells record of anyone left in the field. She won titles here in 2012 and 2016, and is seeking to build some late momentum in what's been a stop-start season. The former World No.1 has a 25-8 record in 2021, but injuries and illness have necessitated five mid-tournament withdrawals.
"It's not that often that I get to play somebody from my country, except Aryna [Sabalenka]," Azarenka said after beating Petra Kvitova in the third round.
This will be a first-time meeting with Sasnovich. Azarenka's tour-level record against her countrywomen is 5-4, with Sabalenka accounting for three of those losses.
 Jessica Pegula (USA) vs.  Elina Svitolina (UKR)
A breakthrough run is one thing; backing it up with consistency is quite another. Pegula has done both those jobs well in 2021. The American has used a maiden Grand Slam quarterfinal run at the Australian Open as a springboard to a 33-18 WTA main-draw record. This week marks the 12th time she has won multiple matches in a tournament, and she will be bidding for her seventh quarterfinal spot of 2021.
Indian Wells is also an event that holds significance in Pegula's career. It was here in 2012 that she made her WTA main-draw debut. A wildcard into qualifying ranked No.305, she navigated through the preliminary competition before falling 5-7, 6-3, 6-3 to Magdalena Rybarikova in the first round.
Highlights: Svitolina d. Cirstea
The winner of this match will receive a significant boost in the Porsche Race to the WTA Finals. Pegula is currently in 14th spot, while Svitolina is just ahead of her in 12th place. The prospect of qualifying for the end-of-year showdown is one that has historically triggered a Svitolina surge. In 2018, she was the joint-last qualifier to be announced - and then promptly won it. In 2019, she was the seventh player confirmed for the eight-woman field, then reached the final.
Svitolina will also be boosted by memories of a career-best semifinal run in Indian Wells in her last appearance in 2019.
Head-to-head: 1-1, both this year. Svitolina defeated Pegula 6-4, 6-3 in the first round of Abu Dhabi, the first tournament of 2021; a month later, Pegula took revenge 6-4, 3-6, 6-3 in the fourth round of the Australian Open.
Shelby Rogers (USA) vs.  Leylah Fernandez (CAN)
Like Emma Raducanu, all eyes were on Fernandez to see whether she could back up a breakthrough. Fernandez, the US Open runner-up, is competing for the first time since a fairytale run in New York
At Indian Wells, she has picked up exactly where she left off by winning thrilling three-setters against higher-ranked opponents under night lights. She needed 2 hours and 41 minutes to get past No.9 seed Anastasia Pavlyuchenkova in the third round.
Highlights: Fernandez d. Pavlyuchenkova
For Rogers, there will be an element of déjà vu to the match. It is the second time within a month she has reached the last 16 of a big tournament on home soil. At the US Open, she followed up an upset of World No.1 Ashleigh Barty with a straight-sets loss to Raducanu. Here, Rogers' path was eased by the last-minute withdrawal of slated second-round opponent Belinda Bencic, who had been the No.8 seed. Faced with New York's other breakthrough teenager, can she reverse that result?
Head-to-head: 1-0 to Rogers, who won 6-2, 7-5 in the second round of Lexington 2020. Neither player was ranked inside the Top 100 at the time. Rogers would upset Serena Williams in the quarterfinals in her next match.
 Jelena Ostapenko (LAT) vs.  Iga Swiatek (POL)
This will be a clash of two players who won their lone Grand Slam titles at Roland Garros, where they both entered the tournament as unseeded teenagers ranked outside the Top 40.
While Ostapenko has yet to win a second major title, she can certainly claim to be a trendsetter. In 2017, she became the youngest Grand Slam champion in 11 years with her phenomenal Parisian run. It was a harbinger of things to come.
In Ostapenko's wake, fellow generation 1997 standout Naomi Osaka followed, winning her first Slam (and just second title) at the 2018 US Open. Since then, we've also seen Bianca Andreescu conquer the US Open in her debut, in 2019, while Swiatek demolished the 2020 Roland Garros field. And, of course, Raducanu, who at this year's US Open became the first qualifier to win a major.
Swiatek has settled smoothly into her position at the top of the game. In her sophomore season, she has put together a 35-12 record, including titles in Adelaide and Rome. She has been near-untouchable this week in her Indian Wells debut, conceding just five games combined, against Petra Martic and Veronika Kudermetova.
By contrast, the four years since Ostapenko's shock title run have been more unpredictable. Yet in recent months, there have been some indications she could be developing some consistency. She won a title in Eastbourne and followed it up with a run to the final in Luxembourg. This week, she has dispatched two tricky opponents in Hsieh Su-Wei and Yulia Putintseva.
Head-to-head: 1-0 to Ostapenko, a 6-0, 6-2 rout in the first round of Birmingham 2019 on grass.