Jannik Sinner and Carlos Alcaraz survived US Open first-round wobbles on Tuesday to stay on course for a semifinal showdown.

World No 1 Sinner fought back from a set and a break down to defeat 140th-ranked Mackenzie McDonald in his first match since being embroiled in a doping test controversy.

Third seeded Alcaraz overcame a second-set blip to defeat 186th-ranked qualifier Li Tu of Australia 6-2, 4-6, 6-3, 6-1.

Italian Sinner battled to a 2-6, 6-2,6-1, 6-2 win over American opponent McDonald in Arthur Ashe Stadium, racing away with 18 of the last 22 games.

The 23-year-old was returning to action just a week after it was revealed that he had failed two drug tests in March. However, he escaped a lengthy ban when officials decided he wasn't at fault for the presence of clostebol, a banned anabolic agent, in his system.

"The response from fans, I feel it has been great, also throughout when the news came out, in the practice sessions, there was a lot of support," said Sinner.

"It's still a little bit difficult. You have to go through day by day."

Alcaraz, who won the first of his four Grand Slam titles in New York in 2022, opened the night session against Tu, who hasn't won a match on the main tour this year.

However, Tu thrilled the crowd as he went about his task of facing a player who is attempting to become only the third man in the modern era to win the French Open, Wimbledon and US Open in the same year.

After being outplayed in the opening set, Tu leveled the tie on a fifth set point in the second.

Alcaraz, however, crushed any hint of a shock result by running away with the clash to record his 15th successive Grand Slam match win.

"He surprised me a little bit. In the first set, he was nervous, but after that, he grew into it and played great tennis," said the Spanish star.

Fifth-seeded Daniil Medvedev, who shattered Novak Djokovic's dream of a calendar Grand Slam by claiming the 2021 US Open, went through with a four-set victory over Dusan Lajovic.

Greek 11th seed Stefanos Tsitsipas, who has never made the second week at the tournament, was stunned 7-6 (5), 4-6, 6-3, 7-5 by Australia's Thanasi Kokkinakis.

Stan Wawrinka, the 2016 champion, failed in his bid to become only the third man in last 50 years to win a main draw match at the tournament at the age of 39 or over.

Wawrinka slipped to a 6-4, 7-6 (5),6-3 loss at the hands of Italian qualifier Mattia Bellucci.

Britain's Dan Evans defeated 23rd seed Karen Khachanov 6-7 (6), 7-6(2), 7-6 (4), 4-6, 6-4 in the longest match in US Open history, a five-hour, 35-minute epic.

The final set, in which Evans trailed 4-0, alone took 61 minutes — and was the shortest set they played.

AFP