The Serena Williams of old delights on delirious second night at US Open | Tumaini Carayol

Throughout a breathless, intense first set in what could have been the last singles match of her career, Serena Williams stared down the world No 2, Anett Kontaveit, and responded to her challenge with an immaculate performance on Wednesday.

In the second set, though, she was barely holding on. As she saved a break point at 1-3 with a sweet, curling ace, she raised her hands to the sky, enraged that she could not find that shot each time she served.

If this were any other 40-year-old, with the rust of a one-year layoff and the nerves of her final event, such shortcomings would be expected. But this is Serena Williams. She not only held herself to stratospheric standards, but somehow fully met them during the delirious second night of her Arthur Ashe Stadium residency. In defeating Kontaveit 7-6 (7-4) 2-6, 6-2, she delayed her singles retirement for at least another round by producing another legendary moment in a career filled with them.

After the pageantry of her opening-round win, with its on-court ceremony and a Billie Jean King speech, the second round felt different. The crowd was slightly more muted, not merely there to say goodbye, and Williams was laser-focused. She was immediately locked in during an intense first set, one filled with quality shot-making from both but dominated by the Williams serve – she is still the best at that. Under suffocating pressure, she sealed the tiebreak as she has done so many times over the years, with an unreturned serve followed by an ace.

To her credit, Kontaveit played a flawless second set, flashing winners off both wings and kissing lines, but Williams simply responded by further elevating her level and managing the match supremely well. By the final games, she had taken full control of the baseline and obliterated Kontaveit’s serve.

It is an achievement all the more remarkable considering her limitations. Her first serve was mesmerising, but averaged only 99mph in the first set – she has not served much under pressure this past year so was initially extremely careful, prioritising precision and percentage over power.

Her movement, historically one of her greatest assets, is notably diminished, but she still found a way to dig out a 19-stroke rally deep in the third set when she most needed to. Despite her lack of match-fitness, she was a rock in the decisive moments.

Over the course of two hours and 27 minutes, she played all the hits at least one more time: the aces and vicious return winners that she saved for important points, the roars and the anguish alike, her heart laid out on her diamond-encrusted sleeves. Halfway through the third set, Williams became frustrated by the electronic line-calling and let the umpire, Alison Hughes, know. She then returned to the baseline and channelled the anger into her tennis.

It was particularly astonishing considering how far from such form she has looked since she has returned. Williams lost in the first round of Wimbledon, was brushed aside with ease by Belinda Bencic in Toronto and then dismantled 6-4, 6-0 by Emma Raducanu in Cincinnati.

She has described the final weeks of her career as extremely difficult to handle. Williams arrived here low on confidence but with one final opportunity to make any impression in the final stretch of her career and no more chances for redemption. The pressure could have been suffocating but, as she has done so many times, she rose to the occasion.

Her success has stemmed from viewing this tournament as a bonus rather than the burden it could have been. “I have had a big red X on my back since I won the US Open in ’99,” she said. “It’s been there my entire career, because I won my first grand slam early in my career. But here it’s different. I feel like I’ve already won.”

She finished with a flourish, tearing Kontaveit’s serve apart in the final game and clinching her victory with a backhand return winner.

The former player Mary Joe Fernandez conducted the on-court interview and her presence alone was a reminder of Williams’s absurd longevity. Fernandez is 51 years old and has been retired for 22 years, but she and Williams were rivals in 1999. She asked Williams if she was surprised by her level on the court, which prompted a laugh and a very pointed stare. “I’m just Serena,” she said.

On Thursday night, Williams was due to return to the same venue, at the same time, alongside her sister, Venus, to compete together in the doubles for the final time, a spectacle that could be even more emotional and compelling than the singles.

Then she will face Ajla Tomljanovic of Australia on Friday. It could be the night she finally says goodbye or the next step in one final legendary run. Regardless, on Wednesday night, she gave the world at least one last demonstration of the unforgettable sight of Serena Williams in full flow.