Defending champion Serena Williams made sure of a place in the semi-finals of the WTA Championships with a 6-2 6-3 win over Petra Kvitova, the 2011 champion, on Thursday.
The American was relentlessly focussed against her gifted Czech opponent, who had led 4-1 in the final set when the two last met, eight months ago in a magnificent match in Doha, but Williams was never headed this time.
Then Kvitova’s angular serving and flat hitting had done constant damage.
Now she was reduced to striking some good blows as an entertaining digression to the flow of heavy winners coming in the other direction.
It lasted only 72 minutes and it was Williams’s third win in the Red Group, leaving her with a day’s rest before she seeks a place in the final by taking on the runner-up in the White Group.
That could be Jelena Jankovic, Li Na, or Victoria Azarenka.
Li Na clinched her second win on Thursday, a 6-3 2-6 6-3 victory over Jankovic.
It was an excitingly unpredictable contest, with Li having three points for a 4-2 second set lead, before losing five games in a row and a great deal of momentum.
She then also let slip a break of serve at 3-1 in the final set to be pegged back to 3-3.
However, she was often the more forceful player off the ground, and her success means that if other results go right, Li may qualify irrespective of the outcome of her last White Group match on Friday, a repeat of the Australian Open final against Victoria Azarenka.
With Jankovic favourite to win her final group match against the winless Sara Errani, it is possible that three players could finish with two wins, which would mean a count-back of the percentage of sets won to decide the two qualifiers.
Angelique Kerber, the last player to qualify for the eight-woman event, kept alive her against-the-odds chances of surviving into the semi-finals from the Red Group.
The Poland-based German overwhelmed Agnieszka Radwanska, the third-seeded Pole who reached last year’ Wimbledon final, 6-2 6-2 in less than an hour.
Radwanska is one of only two players with more than 50 wins on the tour this year – Williams is the other.
But her movement was laboured and her will to influence the outcome of a difficult match ebbed visibly in the second set. After three losses in Istanbul, her season is over.
Kerber still has an outside chance of reaching the last four from her section although that would require a solid win over Petra Kvitova, the 2011 champion, on Friday.