Serena Williams talked us through one of the most striking moments of her US Open second-round upset

• Serena Williams upset World No. 2 Anett Kontaveit in the second round of the 2022 US Open.
• The 23-time Grand Slam champ won the first set with a signature ace in the tiebreak.

NEW YORK — Serena Williams pulled off the seemingly impossible Wednesday night.

Having played only a handful of matches in the run-up to the 2022 US Open, the 23-time Grand Slam champion bested World No. 2 Anett Kontaveit in a grueling second-round thriller under the bright lights of Arthur Ashe Stadium.

The first of the three sets was far and away the most competitive of the match, with the six-time singles champion at Flushing Meadows securing the victory in dramatic fashion: a tiebreak.

Williams and the rising star from Estonia were neck and neck through the first several points, but after "Let's go Serena!" chants reverberated through the arena, Williams began to pull away.

Once the 40-year-old reached set point, the star-studded crowd nearly 30,000 strong erupted and rose to its feet. She rewarded them with a Serena signature: a 91-mph ace that barely nicked the outer edge of the service box.

From the media seats in the second deck of Ashe, Williams looked shocked by what she'd just accomplished.

She froze within a yard of the baseline well after watching the untouched serve fly past Kontaveit, then turned to stare at her box as if to ask her loved ones: "Is this really happening?!"

But 24 years into Williams' professional tenure, we should all know better than to question her self-assurance.

Instead, the greatest champion tennis has ever known said she was merely relishing the moment, standing firm in power while celebrating the feat with clenched fists and silent intensity.

"Very simple: I like to ace when I'm up set point or match point, or hit a winner," Williams told Insider during her post-match press conference. "I was like, yes, I love hitting aces on those types of points."

The family and close friends in her box loved it, too.

Her husband — Reddit co-founder Alexis Ohanian — and mother were joined by the likes of Anna Wintour and Tiger Woods, the latter of whom jumped to his feet and unleashed one of his signature fist pumps upon watching his friend secure the set.

"He's one of the reasons I'm here, one of the main reasons I'm still playing," Williams said after the match. "So we talked a lot. He was really trying to get me motivated."

"When you can rely on someone like that, I mean, my goodness, he's Tiger Woods," she added. "It was really helpful to get clarity."

Williams will return to the court for singles Friday in Flushing Meadows. With a 7 p.m. start, she'll once again play under the lights at Arthur Ashe as she faces World No. 46 Ajla Tomljanović.