Eighth-seeded Karolina Pliskova reached the US Open quarter-finals for a third straight year on Sunday with a 6-4, 6-4 victory over Australian Ashleigh Barty.
The Czech, who won her 10th career title at Stuttgart this year, advanced to a possible quarter-final clash with 23-time Grand Slam champion Serena Williams.
The US superstar was taking on Kaia Kanepi later Sunday, the unseeded Estonian seeking another big upset after toppling world number one Simona Halep in the first round.
One break of serve in each set was enough for Pliskova, whose runner-up finish to Angelique Kerber in 2016 remains her best Grand Slam performance.
She denied 18th-seeded Barty a first major quarter-final appearance.
In a battle of two players among the WTA tour leaders in aces, Barty faltered on serve in the first game, dropping her serve from 40-0 up.
Pliskova, targeting Barty's misfiring backhand, maintained the advantage, and gained the only break she needed for a 2-1 lead in the second even as she saved all eight break points she faced.