INDIAN WELLS, CA, USA - No.1 seed Katerina Siniakova survived a wildly oscillating seesaw of a contest against Sachia Vickery 7-5, 2-6, 6-0 in one hour and 49 minutes to kick off her Oracle Challenger Series Indian Wells campaign and move into the third round.

The Czech, playing her first tournament beneath the main WTA Tour since the Olomouc ITF W80 in July 2018, would have her work cut out for much of a match between two players renowned for their speed and scrappy fighting qualities, but ultimately pulled away in a dominant decider to set up a tantalizing last-16 clash against two-time Grand Slam finalist Vera Zvonareva. 

World No.156 Vickery's career-best win had come in Indian Wells two years ago, when she upset the then reigning Wimbledon champion Garbiñe Muguruza in the second round of the Premier Mandatory tournament, and the American was primed to score another upset today as she leapt out to a quick 3-0 lead - only to see Siniakova strike back to take eight of the next 10 games, sealing the first set and the first break of the second.

Raising her first serve percentage from 61% to 71% was the foundation of Vickery wresting the momentum back as the 24-year-old former World No.73 turned the second set around, winning 16 of the last 20 points as she forced a decider - but there, that number would drop to 59%. Siniakova took control again - particularly on return, where the World No.53 would allow Vickery just four points - to rattle through a bagel set.

A matchup between two former Top 5 players saw Zvonareva overturn a lopsided head-to-head to upset No.15 seed Samantha Stosur 4-6, 6-2, 6-2 - just her second win over the Australian in 10 meetings, and her first in nearly 16 years. Zvonareva had been the victor in their first ever encounter, all the way back in the first round of Wimbledon 2004 - but Stosur would go on would go on to dominate their rivalry with eight straight wins across every surface between 2007 and 2011, including in the 2011 US Open quarterfinals en route to her first major trophy. Today, though, Russian World No.319 Zvonareva finally found the answer to move through in two hours and 14 minutes.

Elsewhere, former junior World No.2 Wang Xinyu impressed with her power game as she scored a 7-6(7), 6-2 victory over former World No.9 CoCo Vandeweghe. The 18-year-old would find herself pegged back in both sets after early breaks, but displayed greater control over her groundstrokes to edge a tight opening set - despite double faulting on her first set point - and then to take charge of the second, racing through 16 of the last 21 points as the American's errors began to flow. Next up for the Chinese teenager will be No.3 seed Bernarda Pera.

First-round action also saw victories for two former Top 30 players on the comeback trail, Irina-Camelia Begu and Lesia Tsurenko. Three weeks ago, the pair had faced each other in the Cairo ITF W100 final, with Begu winning 6-4, 3-6, 6-2, and today both made positive starts to their desert campaigns. Tsurenko, who was sidelined for six months last year due to an elbow injury, moved past qualifier Danielle Lao 6-3, 3-6, 6-1, while Begu overcame Mona Barthel - another former Top 30 competitor recently returned from a six-month hiatus, due to a foot injury in the German's case - 6-4, 6-1 in one hour and eight minutes. The Romanian will now face No.4 seed Taylor Townsend in an intriguing second-set tilt.

There were mixed fortunes for the seeds opening their campaigns in the second round following first-round byes: No.7 seed Madison Brengle was the highest-ranked casualty, losing the longest match of the day 6-7(4), 7-6(2), 6-2 to 2009 US Open semifinalist Yanina Wickmayer in two hours and 37 minutes. However, No.5 seed Laura Siegemund withstood a second-set fightback from Harriet Dart to progress 6-2, 7-5, while Auckland runner-up and No.9 seed Jessica Pegula squeezed past Natalia Vikhlyantseva 6-4, 7-6(5).