With his serving once again letting him down badly, Australia's No.1 was still left reflecting on golden opportunities missed as he went down 4-6 7-6 (9-7) 7-5 7-6 (7-4) to Felix Auger-Aliassime in a curiously uneven and largely flat US Open quarter-final marathon.
After five previous last-eight disappointments while searching for that elusive breakthrough, de Minaur was a set up, then a break up before missing out on a set point in the second, and still looking the better player in the latter stages of the third as he rallied impressively.
There was, as usual, nothing wrong with his spirit as he roared back and looked in complete control of the fourth, at 5-2 up, but when it was time to really come up big after a match of disappointing quality, Auger-Aliassime was the one who soared to the occasion.
"Right now I'm looking at this like a wasted opportunity. It's tough," de Minaur said.
"There's no other way I'm probably going to deal with this, but just seeing it straight, and that's what today was. Today was an opportunity to break new ground. I was nowhere near the level I needed to be at.
"That's frustrating because you don't get these chances often."
With both men often seeming fazed by the magnitude of the occasion, 25th seed Auger-Aliassime, seeking his first semi-final since his breakthrough at Flushing Meadows in 2021, held his nerve best, producing his finest tennis with his booming forehand in the fourth-set tiebreaker to seal the win in four hours 10 minutes.
But de Minaur, who had bowed out at Wimbledon to Novak Djokovic while bemoaning the poor quality of his serving, will again have to unravel with his team why his first-serve percentage was down at just 42, nowhere near good enough at this level.
"It's just in those big matches, that's the first thing that kind of goes away," de Minaur rued.
"And it's a shame because the only thing it does is it just creates a lot more pressure on everything else.
"As the match goes on, I'm playing with second serves, I'm on the back foot, I feel like I've got to do a little bit more. Then I start missing groundstrokes, which I probably wouldn't do.
"It all comes down to that serve."
For large periods, de Minaur still looked set to prevail but, instead, Auger-Aliassime, ranked No.27 in the world, ended up raising the stakes, unleashing 51 winners with his bigger game to just about outstrip his 50 unforced errors.
Over the past four years in grand slams, de Minaur has beaten 26 players who are ranked outside the top 20, and he's lost only two. Unfortunately, both have been in the quarter-finals of the US Open - to Jack Draper last year and now Auger-Aliassime.
"It feels amazing, four years ago, it feels like more. It's been a tough couple of years but it feels great to be back in the semis," said the one-time wonder boy Auger-Aliassime, who will next play either defending champion Jannik Sinner or 10th seed Lorenzo Musetti, who face off in an all-Italian quarter-final later on Ashe.
ALEX DE MINAUR'S GRAND SLAM QUARTER-FINAL PAIN:
* 2020 US Open: lost to Dominic Thiem (AUT) 6-1 6-2 6-4
* 2024 French Open: lost to Alexander Zverev (GER) 6-4 7-6 (7-5) 6-4
* 2024 Wimbledon: lost to Novak Djokovic (SRB) injured, walkover
* 2024 US Open: lost to Jack Draper (GBR) 6-3 7-5 6-2
* 2025: Australian Open: lost to Jannik Sinner (ITA) 6-3 6-2 6-1
* 2025: US Open: lost to Felix Auger-Aliassime (CAN) 4-6 7-6 (9-7) 7-5 7-6 (7-4)
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