Dayana Yastremska vanquished Venus Williams in a three-set thriller at the Western & Southern Open, while American sensation Coco Gauff fell at the first hurdle.
Yastremska sent former world number one Williams packing in the opening round of the WTA Premier tournament on Saturday.
Maria Sakkari claimed a statement win over teenager Gauff in New York amid the coronavirus pandemic, with the event usually held in Cincinnati.
Meanwhile, former champion Victoria Azarenka earned her first victory of the season.
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YASTREMSKA TOPS WILLIAMS
A marathon 5-7 6-2 7-5 contest went in favour of 16th seed Yastremska, who eliminated Williams at USTA Billie Jean King National Tennis Center.
Ukraine's Yastremska needed two hours, 36 minutes to see off seven-time grand slam champion Williams in their first meeting.
Yastremska – who overcame an injury scare in the first set – will next play Bernarda Pera, who defeated Heather Watson 6-1 3-6 6-3.
A victorious effort by @D_Yastremska
— wta (@WTA) August 23, 2020
The No.16 seed charges back from a set down to overcome Williams 5-7, 6-2, 7-5 at @CincyTennis. pic.twitter.com/RVkNhzLqGE
GAUFF OUSTED
The 16-year-old Gauff was no match for Sakkari, who cruised to a 6-1 6-3 triumph.
Preparing for the upcoming US Open at Flushing Meadows, Gauff was comfortably beaten by Sakkari in just 65 minutes.
"I think I really played a good match. I played a match in Palermo, but for me, it doesn't count. It wasn't even a match [there], the way I played," Sakkari, who hit 14 winners and 21 unforced errors said. "Coming back the way I did, it's really important, and [I take] a lot of confidence from this."
AZARENKA UPSETS VEKIC
Donna Vekic – the 15th seed – crashed out following a 6-2 6-3 loss to two-time Australian Open champion Azarenka.
Azarenka, who won the tournament in 2013, needed just over an hour to dispose of Vekic in the opening round.
Next up for Azarenka is either former US Open champion Sloane Stephens or Caroline Garcia.
Moving forward into round 2 @vika7!
— wta (@WTA) August 22, 2020
Azarenka defeats Vekic, 6-2, 6-3 at @CincyTennis. pic.twitter.com/69Nm1W45zo
Elsewhere, ninth seed Elena Rybakina lost 7-5 7-6 (8-6) to Ekaterina Alexandrova, while 11th seed Alison Riske went down 6-3 6-3 against Amanda Anisimova.