NEW YORK -- Serena Williams' yells of "Come on!" crescendoed right along with the tension in a fourth-round US 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 on 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 wasn't an easy match at all. She obviously knows how to play," said Williams, 36, a six-time US Open champion who finished with more than twice as many winners as Kanepi, 47-22. "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. In the 18-minute shutout of the first set, Kanepi was tight, and Williams was pretty much perfect, grabbing 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 has 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 the first day 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 the American began making more and more mistakes.
"I made one or two crucial errors, and that cost me the second set, or at least cost me the first game," Williams said. "Then she [Kalepi] was holding pretty well at that point. So it wasn't like my level went down tremendously. It was one or two points that made a huge difference in that second set."
When Williams shanked a backhand return of a 103 mph serve, the match was a little more than an hour old, and it was tied at a set apiece. That was the first set Williams lost against Kanepi in the 10 they'd played to that point and the first set Williams lost at the 2018 US Open, a run that included a 6-1, 6-2 victory over 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.
Williams is now making her 15th US Open quarterfinals appearance, breaking a tie with Martina Navratilova for the second-most among women in the Open era. Chris Evert's 19 are the most.
Next comes a quarterfinal against 2016 runner-up Karolina Pliskova, who beat Williams in the US 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," the No. 8-seeded 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. I have a game to beat her."
Stephens, 25, had quite a point, one that showed off the best of her versatile game, and so a reporter began recounting what happened.
Stephens interrupted. She did not think the retelling did it justice. At all.
"You are not describing that point good. But I know what you're talking about," Stephens said, then proceeded to give her own play-by-play.
"She hit a drop shot. I hit a drop shot back. Then she lobs me to my forehand. I ran back and hit a forehand crosscourt -- and the crowd went crazy," she said. "You didn't describe it like that. You were getting lost in there. I think that was a great point."
It certainly was. And that chase-down, turn-around, hook-shot of a passing winner showed a glimpse of how the No. 3 Stephens can go from defense to offense with flair, as she did repeatedly during her 6-3, 6-3 victory over No. 15 Elise Mertens of Belgium in the fourth round.
There were other, similar efforts of that sort by the American -- not that she works on those kinds of improvisational moves while training.
"Never, never, never. I'm the type of person, if the ball goes over my head, I'm like, 'whatever,' in practice," she said. "I don't practice that. I think it makes it unnatural. It makes you try to do too much if you're practicing trick shots. I don't know how [Nick] Kyrgios and guys like that do it."
"Just like I always say: Get your racket on it. Make a play on the ball. Make your opponent play an extra ball. That's the most important thing to me," she continued. "Sometimes it doesn't have to be the best shot, but making them play another shot, you might get another opportunity. I worked really hard on that instead of trying to hit a trick shot or do fancy stuff. Just simple: Make them play an extra ball, and see what happens."
Now comes a rematch: She'll face No. 19 Anastasija Sevastova of Latvia, the same person she beat in last year's quarterfinals at Flushing Meadows.
Recalling that 2017 victory, decided by a third-set tiebreaker, Stephens said: "I had to dig really deep."
Sevastova advanced Sunday by eliminating No. 7 Elina Svitolina 6-3, 1-6, 6-0.
Information from The Associated Press was used in this report.