Top seed and Wimbledon champion Angelique Kerber beat US Open winner Naomi Osaka at the BNP Paribas WTA Finals Singapore.
Kerber won her Red Group match 6-4 5-7 6-4 in two hours and 30 minutes on Wednesday.
Japanese number one Osaka has lost both of her matches on her WTA Finals debut after losing a crucial break in the seventh game of the final set.
"It was a great match from both of us. It’s a great feeling to, of course, win the match like that." @AngeliqueKerber breaks down her match with Naomi Osaka#WTAFinals pic.twitter.com/TBBKPqfgGp — WTA (@WTA) October 24, 2018
“Naomi is such a great opponent. She played unbelievable and I think we both played on a really high level tonight,” Kerber said on court after the match.
“I think that I started really well, and the second set was a really close set. I had my chances, but she played unbelievable in the important moments, and I think it was just one or two points that decided the match.”
Kerber converted six of her nine break point chances but landed just 44 per cent of her first serves in the final set.
"2 hours and 20 minutes and we were still out there battling."@SloaneStephens breaks down her marathon match with Kiki Bertens. #wtafinals pic.twitter.com/lNzDPE161d — WTA (@WTA) October 24, 2018
Sloane Stephens also beat Kiki Bertens in a late-night thriller.
Number five seed Stephens won 7-6 (4) 2-6 6-3 to finish at nearly 1am local time, meaning the Red Group will remain wide open until the final day of the round robin.
All four players remain in contention for the two semi-final spots, with Stephens topping the Red Group with two wins and Kerber second, Bertens third and Osaka bottom.
Stephens faces Kerber on Friday in the last day of Red Group play.
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