(Photo credit: Robert Deutsch-Imagn Images)

No. 1 player in the world Jannik Sinner of Italy dropped his first set Saturday, but he rallied in familiar dominating fashion to down Canadian Denis Shapovalov 5-7, 6-4, 6-3, 6-3 at the U.S. Open in New York.

Sinner, the defending champion, experienced little trouble in this tournament leading into the match with the 27th-seeded) Shapovalov. But he was put on his heels early on Saturday, falling behind 4-1 in the first set before taking three straight games to even things up at 5-5.

Shapovalov answered with a dramatic back-and-forth victory in the sixth before closing out the set.

Worryingly for Sinner, Shapovalov dominated on aces 15-2 and nearly bested him on winners, falling 31-30.

But the top-seeded Sinner recaptured his usual form by again rallying, this time from down 3-2, to emerge with a 6-4 win in the second set.

'It was a very, very tough match today,' Sinner said following the match. 'I've known Denis for quite a while, so I knew that I would have to play at a high level today. I'm very happy that I managed to win. He started off very well. I just tried to stay there mentally.'

Sinner again fell behind in the third set, with Shapovalov sprinting out to a 3-0 lead, but Sinner responded with six straight wins to take that set. He finally gained the early advantage in the final set, pressing his 3-0 lead into an eventual 6-3 win.

Shapovalov was partly undone by mistakes, enduring 47 unforced errors and nine double faults.

The win for Sinner sets up a second-round match with the winner of the later match between Tommy Paul and Alexander Bublik of Kazakhstan.

In other action, No. 15 seed Andrey Rublev of Russia overcame Hong Kong's Coleman Wong 2-6, 6-4, 6-3, 4-6, 6-3. Rubley had 15 aces and survived Wong's assault of 25.

No. 10 seed Lorenzo Musetti beat fellow Italian countryman Flavio Cobolli 6-3, 6-2, 2-0 with Cobolli retiring with a right arm injury. No. 8 Alex de Minaur of Australia was leading 6-7 (9), 6-3, 6-4, 2-0 in the fourth set when Germany's Daniel Altmaier retired due to a thigh injury.

In unranked battles, Spain's Jaume Munar cruised past Belgium's Zizou Bergs 6-1, 6-4, 6-4, and Swiss qualifier Leandro Riedi was up 5-3 in the first set when Kamil Majchrzak of Poland retired due to a rib injury. No. 435 Riedi owns the lowest ranking of any player to reach the Round of 16 at a Grand Slam tournament since Richard Krajicek at Wimbledon in 2002.

--Field Level Media