NEW YORK — Serena Williams' yells of "Come on!" crescendoed right along with the tension in a fourth-round U.S. Open match that began as a rout and suddenly became riveting.

When she ripped a backhand winner to claim the third set's opening game Sunday, Williams let out her loudest shout of the day, leaning forward and rocking both arms. This turned into a test, and she passed it.

Williams reached the quarterfinals at Flushing Meadows for a 10th consecutive appearance — she wasn't there last year because she gave birth to her daughter during the tournament — by picking her level up after a lull and using 18 aces to beat Kaia Kanepi of Estonia 6-0, 4-6, 6-3.

"It was a 'Serena scream.' I don't try to do it. It just comes out, and it's just emotions," said Williams, a six-time U.S. Open champion who finished with more than twice as many winners as Kanepi, 47-22.

"This is my job and this is what I do. This is how I earn a living. I'm going to do it the best I can," she added. "Winning a big game and a very important game and a really tight game, I think it was just a relief."

This match was filled with big hitting by both women, along with all manner of shifts in momentum and quality of play. In the 18-minute shutout of the first set, Kanepi's strokes were off and Williams' were pretty much perfect as she grabbed 24 of 30 points.

But after compiling 14 winners and only two unforced errors in that set, Williams began making mistakes, becoming less and less comfortable as Kanepi grew increasingly so. Kanepi is ranked only 44th, but she's been a top-20 player in the past and has made it to Grand Slam quarterfinals a half-dozen times. Sure, that's nothing compared to Williams' 23 major titles, but it's something. Plus, it's worth remembering this: Kanepi eliminated No. 1 Simona Halep on Day 1 of this tournament.

In a blink, Williams had a match on her hands. Kanepi was matching Williams' power with booming groundstrokes of her own. She was getting better reads on Williams' serves. And Williams began making more and more mistakes.

When Williams shanked a backhand return of a 103 mph serve, the match was a little more than an hour old, and it was all tied at a set apiece. That was the first set she had lost against Kanepi of the 10 they'd played to that point, and the first set Williams had lost 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.

After that scream-inspiring hold to begin the final set, Williams broke right away to lead 2-0. She then faced a break point, but Kanepi wasted that chance by sending a backhand wide. From there, Williams smacked an ace at 118 mph, followed by a service winner at 113 mph to go up 3-0, and that essentially was that.

Kanepi's take on Wiliams' serve? "Unreturnable," she called it.

Next for the 36-year-old American comes a quarterfinal against 2016 runner-up Karolina Pliskova, who beat Williams 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.

"I know she was the best at that time, but I just wanted to win. So that's why I won, because I believed I have a chance," the No. 8-seeded Pliskova said. "I have a game to beat her."

The other quarterfinal on the top half of the draw will be defending champion Sloane Stephens of the U.S. against No. 19 Anastasija Sevastova of Latvia in a rematch from the same round last year.

Stephens got there by beating No. 15 Elise Mertens of Belgium 6-3, 6-3 at night, while Sevastova defeated No. 7 Elina Svitolina 6-3, 1-6, 6-0.

Recalling her 2017 quarterfinal victory over Sevastova, which was decided by a third-set tiebreaker, Stephens said: "I had to dig really deep."

The defending men's champion Rafael Nadal reached his fourth Grand Slam quarterfinal of the season, and 36th of his career, by getting past Nikoloz Basilashvili 6-3, 6-3, 6-7 (6), 6-4, while No. 11 John Isner of the U.S. made it that far at Flushing Meadows for the first time since 2011. Isner defeated No. 25 Milos Raonic of Canada 3-6, 6-3, 6-4, 3-6, 6-2 and now faces 2009 champion Juan Martin del Potro who pounded 18 forehand winners in a 6-4, 6-3, 6-1 victory over No. 20 Borna Coric and hasn't dropped a set through four matches.

Nadal has been spending a lot more time on court, going four sets in each of his past two outings.

"Now is the moment to make the next step, step forward, play more aggressive. I did a lot of things well during the whole season. (It) is the moment to make it happen again," said the No. 1-ranked Nadal, who has won 26 of his past 27 matches. "I hope to be ready to make that happen."

He gets two days' rest before taking on No. 9 Dominic Thiem for a semifinal berth in what will be rematch of this year's French Open final, which Nadal won in straight sets.

Thiem prevented a rematch of last year's U.S. Open final by eliminating 2017 runner-up and No. 5 seed Kevin Anderson 7-5, 6-2, 7-6 (2).

This will be Thiem's first quarterfinal at a major other than the French Open — and his first match against Nadal on a surface other than red clay.

"On clay, I think it's one of the biggest challenges in sports to beat this guy or to compete with this guy," Thiem said. "I hope that it's a little bit more comfortable on hard court, but I'm not sure."

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