Serena Williams overcame Petra Kvitova in straight sets to book her place in the semi-finals of the WTA Championships.
The defending champion maintained her 100% record in the round-robin stage with a comprehensive 6-2 6-3 victory over Kvitova, who was crowned champion in Istanbul two years ago.
The Czech created three break points in the opening game but could not take any of them, and was then made to pay as Williams broke her serve immediately before going on to dominate the match.
Kvitova still has a chance to qualify for the semi-finals if she beats Germany’s Angelique Kerber on Friday.
In the white group, Li Na beat Jelena Jankovic 6-3 2-6 6-3 but there is still work to do before the fourth seed can book her place in the semi-finals.
Li just needs a set against Victoria Azarenka on Friday, although she is also well aware that a straight-sets loss would leave her vulnerable.
“Of course it was tight but at least it is better than the last two years,” Li said.
“Now I have one foot in the semis but another foot is still out of the door. If I lose easy tomorrow, I already maybe have no chance. So I still have to fight tomorrow.”
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