Czech world No 3 overpowered her Spanish opponent to maintain her quest of reclaiming the top ranking.
WTA Finals: Pliskova hammers Muguruza to reach semi-finals, Williams battles past Ostapenko
Karolina Pliskova secured her place in the semi-finals of the WTA Finals in Singapore with a straight-sets win over Wimbledon champion Garbine Muguruza yesterday.
The world No 3 had already defeated Venus Williams in her opening match of the White Group round-robin ties and saw off Muguruza 6-2, 6-2.
Pliskova continued her momentum with an early break against the Spanish world No 2, before moving into a 3-0 lead and closing out the first set as Muguruza lost serve again.
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The second set looked to be heading towards a rapid conclusion as Pliskova - after saving two break chances in her opening service game - coasted into a 5-0 lead. Muguruza, though, saved three match points to hold serve and then broke back.
However, Pliskova closed out victory in just over an hour when the Spaniard failed to hold as the Czech player reeled off four unanswered points.
“I didn’t play well the last two games of the match, but I’m just happy that I’m through," Pliskova, 25, said. "It was a very tricky match today, we both didn’t play well. It was tough because we waited so long because the match before us was pretty long. I’m just happy that I’m through."
In yesterday's earlier match, Williams battled to victory in more than three hours against French Open champion Jelena Ostapenko, coming through 7-5, 6-7, 7-5.
There were seven breaks of serve in a sporadic opening set, before Latvian Ostapenko, the world No 7, forced a decider following a tie-break after Williams had failed to convert a match point chance.
Both players, though, continued to struggle to hold serve in the deciding set, which the American No 5 seed eventually secured after one hour and 10 minutes.
“Sometimes you need some luck," said Williams, who won the WTA Finals title in 2008. "I don’t know if there was any luck for me tonight – I just had to work hard for every point.
"Everyone is playing well here. It’s not easy to lose the first match, both of us were in the same situation. You have to fight. What else can you do except try to fight to live another day.”
Today's matches see the Red Group take to the court. First up, world No 1 Simona Halep takes on world No 6 Caroline Wozniacki. Both women won their opening matches in convincing fashion, and the winner of this tie will book their place in the semi-finals.
Elina Svitolina, the world No 4, will then face world No 8 Caroline Garcia.