Karolina Pliskova has breezed into the semi-finals from the White Group at the WTA Finals in Singapore after dismantling Wimbledon champion Garbine Muguruza 6-2 6-2.
But the night's matches could not have been more contrasting - earlier on Tuesday, Venus Williams prevailed over Jelena Ostapenko 7-5 6-7 (7-3) 7-5 in one of the longest three-set matches ever at the event.
The results automatically send Pliskova into the semis but they also eliminate Ostapenko, who is now unable to advance despite still having one more round-robin match left.
Williams will now meet Muguruza on Thursday in a rematch of this year's Wimbledon final, but this time it is a sudden-death match to determine who qualifies in second place in the group.
It took Williams 3 hours and 13 minutes to finish the job against Ostapenko, making it the second-longest match at the finals in Singapore and the third-longest at the finals overall.
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The only ones longer were a 3 hour and 29 minute match between Agnieszka Radwanska and Sara Errani in Turkey in 2012, and an encounter between Caroline Wozniacki and Maria Sharapova here in 2014 that lasted 3 hours and 14 minutes.
The competitors broke each other's serve 20 times and many other games went to multiple deuce points.
The match was a see-saw battle from the beginning.
Ostapenko was at one stage leading 5-4 and serving for the first set, but a powerful Williams effort in the 10th game held her opponent to love and levelled it up.
The American then won the next two games to take the set, with an unforced error count of 17-8 against Ostapenko.
The second set went to a tiebreak, which quickly turned sour for Williams.
She failed to win a point on serve as she double-faulted and launched an ill-advised challenge, going down in the tiebreak 7-3.
But after another tense set, the American eventually held on for an exceptionally gritty victory.
Ostapenko acknowledged the poor serving in the match, saying she served best when her back was against the wall.
"Actually when I was love-40 on my serve, I just didn't care anymore and I started to serve much better," she said.
Pliskova won her match in just 62 minutes and said it was tough to have to wait until after 11pm local time to get on court.
"We were waiting so long. There was already match point in the second set (of the previouus match)," she said.
"And then it went so long that we were a little bit both shaky in the beginning of (our) match and a little bit nervous and maybe a little bit tired, as well."
In Wednesday action, Simona Halep will play Wozniacki, and Elina Svitolina meets Caroline Garcia as matches from the Red Group continue.
