Felix Auger-Aliassime staged a New York fightback to beat Alex de Minaur and reach his second US Open semi-final.
De Minaur was bidding to make the last four at a grand slam for the first time at the sixth attempt and he led by a set and a break at Flushing Meadows.
But Auger-Aliassime, who knocked out third seed Alexander Zverev in the third round, responded impressively, battling to a 4-6 7-6 (7) 7-5 7-6 (4) victory in four hours and 10 minutes.
"It was just a lot of nerves today during the whole match," said Auger-Aliassime, who hit 22 aces and 51 winners overall.
"It wasn't pretty at all times. I was willing to dig really deep and do everything I can to stand here right now. It feels amazing.
"Four years ago - it feels like more. It was a tough couple of years but it feels even better now to be back in the semi-finals. The biggest challenges are yet to come but that's what I live for, that's what I train for."
When the Canadian reached the last four in 2021 as a 21-year-old, it appeared he was ready to build on his great promise as a teenager, but injuries and indifferent form have stalled his progress since.
Since his last slam quarter-final at the Australian Open three years ago, Auger-Aliassime had gone out in the opening round seven times, winning just a single match in New York.
But the 25-year-old's talent remained, with a powerful serve and forehand backed up by great athleticism, and here he has once again put himself among the sport's elite.
For much of the contest it was a question of whether Auger-Aliassime would have the patience and belief to overcome the defensive skills of De Minaur, one of tennis' best counter-punchers.
The Australian began the better and showed he could pull off the spectacular as well with a tweener lob in the third game of the second set.
That set, which lasted almost an hour-and-a-half, was key to the outcome, with De Minaur moving 3-2 ahead but immediately pegged back.
Auger-Aliassime saved a set point in the tie-break with an ace and took his second chance when De Minaur netted a backhand.
The Canadian had both the crowd support and the momentum but the magnitude of the occasion was very evident in shaky play from both.
Auger-Aliassime needed two chances to serve out the third set, and De Minaur was then unable to take his chance to force a decider, sending the match to another tie-break.
Just putting the ball in the court was a challenge, with both men serving two double faults - they finished the match with 11 each - but Auger-Aliassime's extra power gave him the vital edge.
