Making her fifth appearance at WTA Finals, bidding to become the first German player to win the title since Steffi Graf in 1996, extended to 7-9 her record at WTA Finals.
Both debutants won their first-ever contests in the season-ending tournament and still have their fate in their own heads, with group leader Stephens facing Kerber on Friday and Bertens up against Osaka.
"In a way I'm proud of myself for being able to make the matches so close without really having a first serve".
"It was great to win such a great match and to be able to look forward to another one in two days from now". "Doesn't matter how the score was, I was just trying to fight until the last point". The victory meant that Kerber stays in the hunt for a semi-final spot with one round-robin match to play.
If three players are tied, the tiebreakers are the percentage of sets won, or, if necessary, the percentage of games won. Kvitova finished the group with three straight losses. "I know it was tough, it was just insane and chaotic, but in the end, she prevailed, and I knew she prevailed because she stayed focused", King added. "She's incredible when she plays right". Since the 2012 Madrid tournament, the two-time Wimbledon champion has won 27 of 29 matches against Czech opponents. It's kind of cool, actually... it won't happen again for a whole other year, but it's kind of cool to just play against the best.
World number six Stephens has moved into pole position after her second straight victory.
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But Osaka, 21, put on another error-strewn performance as she suffered her second straight defeat after the two-and-a-half-hour marathon last night.
"I was really happy to turn this match around", Bertens said.
A demoralized Stephens had no answer and her slump continued into the deciding set, where she was broken in the second game.
It was really sad and to be honest we haven't really spoken about it that much right after, she didn't really want to speak about it and I respect that.
"It was not easy with all the things going on social media and opinions with my physique", Svitolina said.
"I started really well and she started playing better and better and then I dropped a little bit with my intensity", Kerber said. "I've learned there's thousands of opinions, millions of opinions and I need to just do my job".