Austria's Dominic Thiem clinched his first Grand Slam title after a gritty fightback from two sets down stunned Alexander Zverev in the US Open final.
Second seed Thiem, 27, had lost his previous three major finals and looked destined for another agonising defeat.
But 23-year-old Zverev, playing in his first Slam final, became edgy at key moments and Thiem took full advantage.
Both players failed to serve out victory in a tense decider before Thiem sealed a 2-6 4-6 6-4 6-3 7-6 (8-6) win.
Thiem took his third championship point when Zverev pulled a backhand wide, leaving the Austrian - who suffered cramp during the tie-break - falling flat on his back in celebration.
When he climbed back to his feet, he found a gracious Zverev - with whom he is close friends - waiting to hug him at the net.
"I wish we could have two winners today, we both deserve it," Thiem told Zverev, whom he has known since they were juniors.
Thiem is the first player to claim a Grand Slam title from two sets down since Argentine Gaston Gaudio at the French Open in 2004.
It had been longer since anyone achieved this feat in New York, with Thiem emulating American Pancho Gonzales' comeback in 1949.
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Thiem, who remains third in the world rankings, is the first man to win a maiden Grand Slam singles title since Croat Marin Cilic's 2014 US Open victory.
The absence of 2019 champion Rafael Nadal and Swiss great Roger Federer at the behind-closed-doors Grand Slam, plus the expulsion of top seed Novak Djokovic for hitting a line judge with a ball, opened the door for a new name to be etched on to a major trophy.
Thiem took his opportunity to become the first man outside the 'Big Three' to win the Australian Open, French Open, Wimbledon or US Open since Switzerland's Stan Wawrinka triumphed at Flushing Meadows in 2016.
Thiem overcomes edgy start to fulfil Grand Slam dream
While this final was not of the same ilk as some recent Grand Slam classics, it developed into a gripping contest which was impossible to call right up to the very last ball.
Odd moments of brilliance from both players were outweighed by mistakes, with the match eventually won by a battle of the minds as much as their techniques.
Thiem was the favourite to take advantage of the absence of the 'Big Three' and finally land his maiden Grand Slam title.
The Austrian had lost the past two French Open finals to Nadal, who cemented his place as the greatest clay-courter of all-time by winning his 11th and 12th titles at Roland Garros.
Then he lost February's Australian Open final against Djokovic, who claimed a record eighth title in Melbourne.
So this was the first major final where the world number three was not playing one of the game's greats.
Whether his jittery start came as a result of that additional expectation to achieve his ultimate career goal, or perhaps an Achilles injury that bothered him in Friday's semi-final against Daniil Medvedev, was unclear.
Eventually, he settled down to the task after trailing by two sets and a break. Thiem started to land more first serves and find more fizz in his returning game, as well as being aided by Zverev's own edginess starting to appear in the third and fourth sets.
Momentum had now swung back to the Austrian and when he broke serve in the first game of the decider, it seemed like that might have been the catalyst for him to close out victory relatively comfortably.
That was not the case as the drama stepped up. Thiem hit a double fault on break point in the next game, then fought back from 0-30 in the sixth game after a stunning forehand winner down the line.
Little separated the pair as they were locked at 3-3, having won 139 points each in the match, and led to that riveting finale where they split four breaks of serves before the tie-break decided the outcome.
Tearful Zverev falls agonisingly short
Like Thiem, Zverev was also aiming to fulfil his much vaunted potential by winning a first Grand Slam title.
The 23-year-old made a confident start in his first major final as he moved into a two-set lead, but some of his weaknesses - particularly the tendency to hit double faults under pressure - began to appear.
Two double faults in the fifth-set tie-break gave the upper hand to Thiem, who eventually got over the line despite struggling physically in the final moments.
Zverev's heartbreak at the manner of his defeat was clear, breaking down in tears as he struggled through his runner-up speech.
He cried as he tried to thank his parents Alexander - also his coach - and Irina who were not in New York after testing positive for coronavirus.
"I miss them. I'm sure they are sitting at home pretty proud even though I lost. I wish one day I can bring the trophy home," he said.
For so long Zverev had been touted as a major winner but had failed to deliver on the Grand Slam stage.
That was until he reached his first Grand Slam semi-final at the Australian Open earlier this year - where he lost to Thiem - and then backed that up by going one better in New York.
"It was a tough battle and I wish you had missed a little bit more so I could lift that trophy," he told Thiem.
"To my team, the last two years haven't been easy but we are definitely on our way up."
BBC tennis correspondent Russell Fuller
An astonishing Grand Slam final - which had moments of sheer genius, and others which felt like intruding on private grief.
For the first two sets, Thiem was listless and horribly off key; Zverev often excelling in his first Grand Slam final.
The final set produced the best tennis of the match, but also moments of unbearable stress and pressure. Both served for the title, and in the tie-break Zverev's two double faults made the difference, after Thiem looked to have a case of terminal cramp.
Perhaps we underestimated just how stressful it would be to win a Grand Slam in the absence of Djokovic, Federer and Nadal. Without any of them as opponents in the final, neither could pretend they had nothing to lose.
It will be a crushing disappointment to Zverev, but he has reached a semi-final and a final in this year's two majors, with still so much room to improve.
Thiem, meanwhile, is likely to become an even more formidable Grand Slam foe for Djokovic and Nadal.
He will think anything is possible right now, but surely even this extraordinary athlete will need more than 13 days to get ready for another tilt at a major title at the French Open in Paris.