Images from the US Open men's singles first round matches, at Flushing Meadows, New York, on Tuesday.

Carlos Alcaraz was given a scare by Australian qualifier Li Tu in the first round of the US Open on Tuesday before going on to seal a 6-2, 4-6, 6-3, 6-1 victory.

Four-times Grand Slam champion Alcaraz, who lost to Novak Djokovic in the final of the Paris Olympics, got off to a hot start before the errors began to pile up and he dropped the second set.

The Spaniard restored order by whipping a forehand to break in the third for a 4-3 lead and never looked back, sealing the win with his eighth ace to set up a second-round meeting with Dutch player Botic van de Zandschulp.

Tu, an Adelaide native who stepped away from tennis in 2014 for six years to get a degree and start a tennis academy, won three qualifying matches to earn his first appearance on Arthur Armstrong Stadium court against the third seed.

Alcaraz won the French Open in June and defeated Djokovic to triumph at Wimbledon a month later but was left bitterly disappointed after falling short at the Paris Games before suffering a shock defeat by Gael Monfils at the Cincinnati Open.

The 21-year-old, who won the US Open in 2022, showed no signs that his movement was limited by a right ankle injury he suffered during a practice session on Saturday.

Sinner overcomes erratic start to beat McDonald

Top-seeded Italian Jannik Sinner shrugged off the doping furore surrounding him and overcame a bad start to reach the second round of the US Open with a 2-6, 6-2, 6-1, 6-2 victory over American Mackenzie McDonald.

Sinner, who became embroiled in controversy in the week before the year's final Grand Slam after the International Tennis Integrity Agency said that he tested positive twice for an anabolic agent in March, was slow out of the starting blocks.

The Australian Open champion committed several unforced errors in the opening set, which McDonald took full advantage of to claim an early lead.

The American broke early in the second set to take a 1-0 lead, but after spurning three breakpoints in a lengthy game, Sinner levelled at 1-1.

The hard-fought break appeared to fill the world number one with confidence and the tide of the contest turned as he raced to a 4-1 advantage, before holding serve and breaking once again to square the match at a set apiece.

Sinner never looked back from there and won five games in a row to take the third before winning the first three games of the fourth set without dropping a point.

McDonald won a couple of games late in the match to delay the inevitable, but Sinner made his advantage count and served out the set to claim an emphatic victory.

The 23-year-old faces another American, Alex Michelsen, in the second round.

Tsitsipas sent packing by Kokkinakis

Stefanos Tsitsipas's US Open woes continued as he suffered a 7-6(5), 4-6, 6-3, 7-5 defeat to Australia's Thanasi Kokkinakis in the first round on Tuesday.

After losing a close first set in a tie-break, Tsitsipas rallied to win the second and level the match, but appeared to have an abdominal issue late on before slumping to defeat in three hours and 54 minutes.

Tsitsipas, a two-time Grand Slam finalist, has a poor record at Flushing Meadows and has never made it past the third round of the US Open.

He also struggled in the build-up to the tournament, winning just one of his three matches at the Canadian Open and Cincinnati Masters.

For Kokkinakis, it was a first win at the New York Grand Slam since 2019.

"I had a five-set battle with him a couple of years ago at the Australian Open and I was expecting a war," Kokkinakis said, in his on-court interview.

"It was physical out there and I have a tendency to sometimes drag these matches on and have some real long battles, but I just tried to stay focused, stay the course and just tried to play every point."

He next faces Portugal's Nuno Borges, who beat Argentina's Federico Coria 6-2, 6-4, 6-1.