Karolina Pliskova defeated Garbine Muguruza in straight sets on Tuesday to seal top spot in the White Group at the WTA Finals and eliminate Jelena Ostapenko from the end-of-season competition.
World number three Pliskova raced to a 6-2 6-2 victory over the Wimbledon champion, who narrowly avoided suffering a bagel in the second set by finally holding and then breaking her opponent.
But her recovery arrived too late for the Spanish second seed to avoid a seventh defeat in nine career meetings with Pliskova.
Having lost to Muguruza on day one and Venus Williams earlier on Tuesday, this result brought an end to surprise French Open winner Ostapenko's participation in Singapore.
Muguruza made a slow start and was duly punished, giving up a break in her first service game when she dragged a weak backhand into the net.
The Wimbledon champion then failed to take an opening offered up in the next game by Pliskova, who held by coming to the net and forcing Muguruza into a hopeful lob attempt that fell well short.
Pliskova showed no indication of giving up the control she had established, firing off a cross-court backhand winner from a Muguruza second serve to break again and take her second set point.
The Czech dug deep to save two openings and hold in the first game of the second set, before breaking yet again as Muguruza finally attempted to increase her intensity, only to send an overhead smash into open court long.
At 5-0 behind there was a mini-revival as Muguruza finally showed what she is capable of, the 24-year-old saving three match points to hold for the first time in the second set, before breaking Pliskova for the first time in the match.
But she was promptly broken again as Pliskova sealed a deserved triumph in just 62 minutes to advance to the semi-finals.
"I think I played well the last two games," Pliskova said.
"A very tricky match today, tough because we both waited so long," she added, referring to the marathon encounter between Williams and Ostapenko.
Of Muguruza, the Czech added: "She's a great player, a great champion. We always play close. I was expecting a tough one, [I'm] happy it was like this. I made the quick break in both of the sets, I think that was the key."
Pliskova  bt Muguruza  6-2 6-2
Pliskova - 15/8
Muguruza - 7/17
Pliskova - 1/0
Muguruza - 0/2
BREAK POINTS WON
Pliskova - 5/10
Muguruza - 1/4
FIRST SERVE PERCENTAGE
Pliskova - 61
Muguruza - 67
PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Pliskova - 68/65
Muguruza - 55/27
Pliskova - 59
Muguruza - 38