Serena Williams of the United States hits a return during the women's singles fourth round match against Kaia Kanepi of Estonia at the 2018 US Open in New York, the United States, Sept. 2, 2018. Williams won 2-1. (Xinhua/Wang Ying)

NEW YORK, Sept. 2 (Xinhua) -- Serena Williams, No. 17 seed, roared into the U.S. Open women's singles quarterfinals here on Sunday, beating Kaia Kanepi of Estonia 6-0, 4-6, 6-3.

Serena, who missed last year's U.S. Open to give birth to her daughter, smashing 18 aces today to stop Kanepi, who had stunned the top seed Simona Halep in the first round.

"It wasn't an easy match at all. She obviously knows how to play," said Serena, a six-time U.S. Open champion. "I was just happy to get through it."

This was filled with big hitting by both women, along with all manner of shifts in momentum and quality of play. The 36-year-old Serena finished with more than twice as many winners as Kanepi, 47-22.

However, Serena lost her first set at the 2018 U.S. Open, a run that included a 6-1, 6-2 victory over her older sister Venus in the third round Friday night.

In the quarterfinal, Serena will meet 2016 U.S. Open runner-up Karolina Pliskova, who beat Serena in the U.S. Open semifinals that year.

"I really was feeling great that year. I'm feeling great now, too. But it was a little bit different story, 2016. I was, like, a dark horse. Nobody was expecting me to get that far," Pliskova said after beating No. 18 Ashleigh Barty 6-4, 6-4.