NEW YORK, NY, USA - The honors in the first clash of former champions at the 2020 US Open were taken by No.3 seed Serena Williams, who essayed a signature comeback and served 12 aces to overcome No.26 seed Sloane Stephens 2-6, 6-2, 6-2 in one hour and 43 minutes.

In her post-match press conference, Williams said that she "[tried] to stay calm and be more serene" after the loss of the first set. "I just knew it was important for me just to keep trying, just to keep going."

Williams has now lost just once to her American compatriot in seven meetings - Stephens' breakout moment in the 2013 Australian Open quarterfinals - and though the pair had not met since Roland Garros 2015, proved that the intervening half-decade had not affected her mastery of the rivalry. The victory, in a contest whose quality rose as it went on, also preserves the 23-time major champion's near-perfect record of reaching the second week of the US Open: Williams's only loss in Flushing Meadows before the fourth round came in her 1998 tournament debut, to Irina Spirlea in the third round.

"Right now I'm really focused on the US Open, and nothing else I can think about right now," Williams stated.

For a set-and-a-half, though, it looked as though a second loss at this stage could ensue. After a tense start, it was Stephens who settled first off the ground, thriving in longer exchanges in which she was able to open up the court before injecting her signature pace to finish the point. Perhaps surprisingly, the 2017 champion was also the more aggressive off the ground, with Williams caught between safe topspin shots through the middle of the court and higher-risk attempts that too often went wayward.

The former World No.1 particularly struggled when Stephens stretched her out wide, conceding her serve in the third game with three consecutive unforced errors - of which she ultimately tallied 13 in the first set to only 10 winners.

The fifth game would find Williams's trademark serve come to her rescue to fend off two points to go down a double break - but after Stephens had saved two break points of her own in the next game, one with a superb forehand winner, to move 4-2 up, the 27-year-old would control the ensuing passage of play.

Increasingly fluid off the ground, Stephens seemed to have found the perfect balance of consistency and attack as the second set got under way, and a rattled-looking Williams seemed unable to hang with the younger American - at one point wildly slashing at full power on three consecutive returns, none of which were close to finding the court. A double fault from the 23-time Grand Slam champion at 2-2 brought up a point for the surging Stephens to move up a set and break.

But a brace of service winners enabled Williams to stave off danger, and it was Stephens who shanked a forehand to end the game. Suddenly, it was the 38-year-old who had rediscovered her fluidity both in terms of movement and swing: a marvellous lob paved the way to a first break of the Stephens serve for 4-2 as errors crept into her opponent's game.

"I think in the second set, I feel like my serve percentage went up a little more and I had to start making a few more," said Williams. "That definitely helped a lot."

Unleashed - and stemming the flow of her own cheap unforced errors to a stingy five each in the second and third stanzas, a period in which she found 19 winners - Williams stamped her authority firmly on the rest of the set, racing through eight of the last nine points and sealing the set with a purely struck, deeply satisfying angled forehand crosscourt winner on the run.

Williams's improved footwork had enabled a dramatically increased comfort level in extended points - and, no longer able to elicit the same errors as in the first set-and-a-half, it was Stephens whose strokes were now breaking down first. Five errors in the fourth game of the decider - as many as she had hit in the entire first set - put the 2018 Roland Garros finalist down a crucial break, and there was to be no plot twist.

Though Williams's serve had been the best part of her game in the first half of the match, only in the second and third sets did it reach its most formidable level. Her final two service games found the six-time US Open winner sending down aces and service winners as though they were routine.

As if to underline her turnaround in form, the last game found Williams striking out on return with the same force as she had at her nadir in the second set - and this time, it fizzed across the court for a sumptuous winner. Two points later, with Williams stepping into the court and taking the ball on, it was the higher seed who had sealed the win - and set up another intriguing matchup in the fourth round against No.15 seed Maria Sakkari, her conqueror in Cincinnati last week.

"I don't think it's anything tricky," said Williams, regarding playing the same opponent in back-to-back weeks. "Especially when you lost, it's good to kind of go back out there and try to do a little bit better."

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