This time in NYC, at the US Open, Serena Williams beats Maria Sakkari

NEW YORK—They exchanged sets, then they exchanged breaks. And at the end of a compelling and competitive decider, they exchanged victories.

Serena Williams atoned for her loss to Maria Sakkari at the Western & Southern Open—a match held two weeks earlier in Flushing Meadows, and a match that saw the 23-time Grand Slam champion disintegrate in the third set—by defeating the 15th-seeded Greek at the US Open, 6-3, 6-7 (6), 6-3.

Today's third set couldn't have gone differently for Williams, though she trailed it 2-0. For one, she was engaged throughout. But more importantly, from a break of serve down, the 38-year-old summoned the type of clutch serving and measured aggression that has defined her career at the majors. The win was Williams' record-extending 100th in Arthur Ashe Stadium, and she's now three more away from capturing elusive No. 24.

"Second set, Sakkari turned it up," says Martin Blackman, the USTA's General Manager of Player Development and who was one of the few seated in Ashe. "[Williams] had to be more aggressive, she realized it. Maybe Serena didn't pick on her forehand as much in the second set. Even though Sakkari can really attack off that side, that's a side that can go off a little bit, too.

"Serena found another gear. Just showed why she's the greatest of time."

Same setting, different result. Serena Williams earned some revenge against Maria Sakkari on Monday afternoon. (Getty Images)

Unlike Williams' previous match in Ashe, against Sloane Stephens, both competitors regularly played well at the same time. The rallies were fierce, and winners were often demanded to end them. Sakkari struck more—35 to 30—and Williams only landed 54 percent of her first serves in. The fact that Williams finished the match winning eight more points—and finished on top, period—speaks to her play during the most pivotal sequences.

"She just turned it up, taking the ball earlier, attacking Sakkari's second serve," says Blackman. "First-serve percentage went up; her serve-plus-one and return-plus-one became a real weapon, and she just never looked back. She's just such a good closer."

The most critical sequence came at 3-3 in the third, after Williams fought her way back from an early deficit. It was not unlike the second-set tiebreaker, which Williams trailed 0-4 but recovered all the way to 6-6, before Sakkari took the final two points. This time, Williams' commitment on her biggest shots—serve, forehand, backhand; in short, all of them—helped push her ahead of Sakkari.

But there was something else, according to Blackman: Williams' movement, which the Bronx, N.Y. native sees as the key to unlock Serena's title-winning potential.

"My biggest takeaway, over the course of this tournament, is how well she's moving," he says. "She's moving really well in the corners, adjustment steps, into the court, backing up when she needs to."

Williams pounced on short balls and traversed the hard court inside Arthur Ashe Stadium with confidence and command. (Getty Images)

As the games moved along, the pressure rose, but Williams never grew tentative, aiming for the corners with her crosscourt backhand and taking her forehands early and deep. There were no signs of the self-doubt that has damaged Williams on multiple occasions already this summer.

After a forceful hold and celebratory yell for 4-3, Williams brought out her weaponry in what would be Sakkari's final service game. At 0-30, she annihilated a second serve with a backhand return winner, and though Sakkari would fight off two break points, the third proved too much to handle, just as Williams was today.

Serena's showing may be even more impressive considering the vacuum in which she played. With no fans showering her with applause—though there was certainly some vocal Serena support inside Ashe—Williams had to generate any energy needed to see her through to the quarterfinals, where she'll face either Alize Cornet of Tsvetana Pironkova.

"I think if anybody can adapt to adversity, it's Serena," says Blackman. "She's proven that throughout her career. I actually think it gives her an advantage, because of how mentally tough she is.