NEW YORK: 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 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, who he 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.