On the second day of the Akron WTA Finals Guadalajara, Group Chichén Itzá's opening matches reprise some of this season's key contests. Will the narratives set earlier in 2021 be underlined - or switched around?
Named after the ancient Mayan city on the Yucatán Peninsula, Group Chichén Itzá features four players who have taken control of their own storylines in 2021. Aryna Sabalenka attained the consistency that had eluded her in the past, and enjoyed long-awaited Grand Slam breakthroughs. Iga Swiatek acquired the authority of a top player after her stunning Roland Garros title run in 2020. Maria Sakkari levelled up to reach two major semifinals. And Paula Badosa broke through on clay - then did it again on hardcourts.
 Maria Sakkari (GRE) vs.  Iga Swiatek (POL)
Among Sakkari's many notable accomplishments in 2021 is her proficiency in snapping streaks. In the Miami quarterfinals, she ended Naomi Osaka's 13-month, 23-match winning streak in breathtaking fashion, 6-0, 6-4. In the US Open fourth round, she inflicted Bianca Andreescu's first US Open main draw loss in 11 matches, triumphing 6-7(2), 7-6(6), 6-3 in a three-and-a-half-hour late-night marathon.
And in between, she ended Swiatek's Roland Garros title defence, ending the Pole's 11-match, 22-set Parisian streaks in the quarterfinals 6-4, 6-4. Three months later, Swiatek had still not solved Sakkari, whose 6-4, 7-5 victory in Ostrava snapped her own nine-match losing streak in WTA semifinals.
Those matches encapsulated both Sakkari's existing strengths, and what she has added to transform her game this season. The Greek's fitness has never been in question, but from her first tournament of 2021 in Abu Dhabi, it was clear Sakkari was now in possession of a newly formidable serve and a commitment to a revamped, aggressive game.
With two titles and second-week showings at all the Grand Slams, Swiatek's first season after becoming a major champion contained few disappointments. The 20-year-old has proved to be a quick problem-solver, both within matches and when it comes to the demands of the tour - though she says herself that there's still some way to go.
"I played some tournaments I've never been to," she told press. "Being seeded there was pretty weird. ... I would say the most tricky thing was learning how to play with the higher ranking because usually I was an underdog. I still feel like I didn't figure it out completely."
The challenge of Sakkari has thus far eluded her, and rectifying that will be high on Swiatek's list of priorities. Her ability to bring something different to the matchup will be key.
A third victory over Swiatek for Sakkari would send a message that her presence at the WTA Finals isn't just because she's an upset artist, but because she belongs at the table herself.
An advantage for Swiatek could be her preparation. Following Indian Wells, she remained in the United States to practice - and did so at altitude after doubles partner Bethanie Mattek-Sands invited her to Phoenix.
But it was Sakkari who summed up what could be a crucial attitude to the Guadalajara conditions in her pre-tournament press conference.
In a flashback to her days as a baseline grinder who relied on her fighting spirit, rather than her big serve and forehand, to win, she told press: "It's just whoever accepts the most mistakes, whoever accepts playing ugly tennis this week - 'ugly', you know what I mean - will give herself a better chance on winning the tournament."
Head-to-head: 2-0 to Sakkari, both matches this year.
 Aryna Sabalenka (BLR) vs.  Paula Badosa (ESP)
When Paula Badosa edged out Aryna Sabalenka with a narrow 5-7, 6-2, 7-6(4) victory in the second round of Cincinnati in August, the result was arguably the first indication that the Spaniard's stellar clay season was no flash in the pan.
The North American summer hardcourt swing was arguably Badosa's toughest portion of the year. Over the course of the clay and grass swings, she had surged from outside the Top 70 to inside the Top 30 thanks to a series of stellar results: a Madrid semifinal, a maiden title in Belgrade, a quarterfinal at Roland Garros and the fourth round of Wimbledon.
But her Olympic dream had ended in unfortunate fashion in the quarterfinals against Marketa Vondrousova: suffering from heatstroke, Badosa had to leave court in a wheelchair. Immediately afterwards, she abruptly split from coach Javier Marti, whom she had credited for her rise. During August, she was also beset by a shoulder injury.
Defeating Sabalenka, her third Top 10 win of the year, was a statement that Badosa would not let these setbacks slow her down, and it presaged her phenomenal run to the Indian Wells title in October. She has not competed since then - though told press that she "didn't relax so much" - and enters the WTA Finals on a six-match winning streak.
By contrast, Sabalenka was in Indian Wells, but not in the draw. She was laid up in her hotel room for 10 days, having tested positive for Covid-19.
"For four days I was really sick," she said. "I couldn't move. After four days, it was all about the quarantine. I stay in the room for 10 days. I was doing some workout there, but it wasn't enough. It's not so much space, you cannot move. You just stay in one place and do floor exercise. Honestly, it's not really helping that much."
That experience left Sabalenka ill-prepared for her only other tournament of the autumn in Moscow, but may have been a blessing in disguise. Having racked up a 43-16 record through the US Open, her lack of match play since does mean she's feeling refreshed and "ready to go".
Neither Badosa nor Sabalenka have been satisfied with their adjustments to the altitude of Guadalajara yet: "I was shocked that I cannot control anything," said Sabalenka. But the Belarusian does have experience of winning above sea level: one of her most impressive tournament victories of the year was in Madrid, where she used her power advantage to swat aside the rest of the draw.
For Badosa, a key to victory could be whether she is able to take Sabalenka the distance. Thirteen of Sabalenka's 16 losses this year have been in three sets, and they outweigh her nine wins in deciding sets: while her dominance over opponents she can blow away in straight sets is undeniable, once in a final set the result becomes more of a toss-up.
By contrast, third sets are where Badosa thrives. Her record in three-setters this year is 14-6, and the last of those was a superb test of her fortitude in the longest final of 2021, defeating Victoria Azarenka 7-6(5), 2-6, 7-6(2) in Indian Wells.
Head-to-head: Badosa leads 1-0.
AKRON WTA FINALS GUADALAJARA: DAY 2 ORDER OF PLAY
Starting at 2pm
 Maria SAKKARI (GRE) vs  Iga SWIATEK (POL)
 HSIEH Su-Wei (TPE) / Elise MERTENS (BEL) vs  Alexa GUARACHI (CHI) / Desirae KRAWCZYK (USA)
Not before 7.30pm
 Aryna SABALENKA (BLR) vs  Paula BADOSA (ESP)
 Barbora KREJCIKOVA (CZE) / Katerina SINIAKOVA (CZE) vs  Sharon FICHMAN (CAN) / Giuliana OLMOS (MEX)