Hard work, but Spanish ace proves Tu good for Aussie

Carlos Alcaraz was given a scare by Australian qualifier Li Tu in the first round of the US Open before going on to seal a four-set victory.

Four-time 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 win 6-2 4-6 6-3 6-1 in New York on Tuesday (Wednesday AEDT).

His victory 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 Ashe Stadium against the third seed.

"Obvious he surprised me a little bit," Alcaraz said in an on-court interview with another Australian Nick Kyrgios, who is working at Flushing Meadows as an ESPN analyst.

"He started the match a little nervous but after the first set he grew up, he started to play great tennis.

"Now I'm going to follow him and his results because I'm pretty sure I'm going to be seeing him around very, very soon."

Alcaraz won the first set with ease and the subdued crowd appeared to resign itself to a one-sided match.

However, Tu turned the tables with a passing shot that flew by the charging Alcaraz for a 5-4 lead in the second and broke serve with a beautiful one-handed backhand down the line to level the contest, raising his hand to his ear as the crowd came to life.

Alcaraz's power began to wear Tu down in the third set in hot and humid conditions and the 21-year-old went on to claim the win.

The Spaniard won the French Open in June and defeated Djokovic to triumph at Wimbledon a month later, so this victory extended his grand slam winning streak to 15 straight matches.

In other matches, top-seeded Italian Jannik Sinner shrugged off the doping furore surrounding him and overcame a bad start to reach the second round.

Australian Open champion Sinner kicked off his campaign at the year's final major with a 2-6 6-2 6-1 6-2 victory over American Mackenzie McDonald.

Sinner became embroiled in controversy in the week before the Open started after the International Tennis Integrity Agency said he tested positive twice for an anabolic agent in March.

The Italian, who has denied wrongdoing, has been under intense scrutiny in New York and was slow out of the starting blocks, before finishing strongly.

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

In other first-round action, Britain's Dan Evans came through a marathon contest lasting five hours and 35 minutes, the longest ever match of the tournament in the professional era, to beat 23rd seed Karen Khachanov 6-7 (6-8) 7-6 (7-2) 7-6 (4-7) 4-6 6-4.

Russian fifth seed and former champion Daniil Medvedev overcame a second-set wobble to beat unseeded Serbian Dusan Lajovic 6-3 3-6 6-3 6-1.

Czech 18-year-old Jakub Mensik knocked out Felix Auger Aliassime, beating the Canadian 19th seed 6-2 6-4 6-2.

Jack Draper also reached the second round after his Chinese opponent Zhang Zhizhen retired with a left leg injury in the third set with the Briton leading 6-3 6-0 4-0.

Frenchman Arthur Fils beat American Learner Tien 6-4 3-6 6-1 6-2, and 16th-seeded American Sebastian Korda scored a 7-6 (7-3) 6-1 6-0 victory over Corentin Moutet, of France.

And Swiss veteran Stan Wawrinka failed to make the most of his main-draw wildcard, the three-time grand slam champion losing 6-4 7-6(5) 6-3 to Italian Mattia Bellucci.