The U.S. Open was Nick Kyrgios’ to win, but instead of leaving Flushing Meadows with his first Grand Slam title, he left having flushed a major opportunity down the toilet and with a trail of debris for someone else to clean up as usual.

For all the progress the 27-year-old Aussie has made over the past few months — he arrived in Queens having won more matches since the French Open than any player on tour, which included winning the singles and doubles titles on the same day at last month’s Citi Open in Washington D.C. — it felt as if he erased much of it in eight seconds. That’s how long the Mount Saint Nick eruption lasted after a five-set loss to Karen Khachanov in the early-morning hours Wednesday, when he obliterated two rackets in a post-match fit of rage that would have made Bobby Knight blush.

He at least got the anger out before his post-match press conference, so maybe it accomplished something.

“I honestly feel like s–t,” said a sullen Kyrgios, who could barely lift his head high enough to reach the microphone. “I feel like I’ve let so many people down. … I feel like these four tournaments [Grand Slams] are the only ones that ever are going to matter. It’s just like you got to start it all again. I have to wait till [the] Australian Open. It’s just devastating.”

And it makes you wonder whether Kyrgios, who is always teetering on the brink of an eruption, will ever be able to recapture the consistency and discipline that he displayed over the last few months.

He’s also facing some turbulence in his personal life. Accusations of domestic violence — dating back to 2021 — emerged during Wimbledon from his ex-girlfriend Chiara Passari and he is due in court in October.

On the court, though, Kyrgios had never made it out of the third round in eight previous appearances at the U.S. Open — much less to the precipice of the semifinals — and this trophy had his name on it with the way he was playing.

Two-thirds of the Big Three weren’t here. The other member, Rafael Nadal, was playing for the first time since an abdominal tear knocked him out of Wimbledon, then was knocked out in the fourth round earlier this week by Frances Tiafoe. Kyrgios had a clear path to the final, especially after he beat world No. 1 Daniil Medvedev in impressive fashion in his previous match Sunday.

He’d also been building toward a title run, displaying a kind of consistency, discipline and maturity that was never previously part of his otherwise uber-talented game, which has the potential to be as good anyone’s in the world.

There’s the booming serve, yes, and the genius creativity has always been there, too. But his backhand had developed into a weapon since his first Grand Slam final earlier this summer at Wimbledon, where he held himself together for a set before imploding against Novak Djokovic. Other parts of his game rose in consistency and effort, too, from footwork, to ground strokes, to point construction. Even the expletive-laced explosions seemed to simmer.

Until they didn’t.

Kyrgios came out “flat” and said he “physically didn’t feel great” in dropping the opening set against Khachanov. Two fans were also kicked out after one gave the other a haircut in the stands. And Kyrgios got a visit from the trainer for a sore knee, though that wore off.

Still, in a night of aces — a combined 61 in all — the kind of tennis that Kyrgios had been playing lately started to show up in spades. He took the second set, 6-4, then, after losing the third, 7-5, won a jaw-droppingly good fourth set in a tiebreak.

Yet it was the hard-hitting Khachanov, twice a quarterfinalist in majors (one of them a loss to Kyrgios in Australia) and once ranked as high as No. 8 in the world, who showed the kind of resolve that Kyrgios has long been criticized of lacking. Khachanov had 31 unforced errors to Kyrgios’ 58, and the big Russian saved seven of the nine break points he faced on the night.

Kyrgios, meanwhile, took a step backward, again.

After badly misfiring on one of those on-the-tee forehands during a break point opportunity at 4-4 in the third, the combustible Aussie spiked his racket. Then, after losing the set, he threw a drink during the changeover, earning a warning for unsportsmanlike conduct.

Sure, there were glimmers of possible resolve along the way — Khachanov got within two points of victory in the fourth set only to be thwarted — but Kyrgios never seemed fully in control. He got broken in the fifth and when the match ended his temper couldn’t be contained any longer.

“I saw after the rackets were flying,” Khachanov said. “But I feel the pain for him, yeah.”

Not as much as the three rackets Kyrgios busted up.

“Pretty much every other tournament during the year is a waste of time, really,” he said. “You should just run up and show up at a Grand Slam. That’s what you’re remembered by.”

Except for Kyrgios, who with a few seconds of rage further cemented his reputation as a hothead and destroyed all the hard work he’d put in the last few months.