Spain's Carlos Alcaraz was knocked out of the US Open on Friday, as the final Grand Slam of the year lost one of its biggest crowd-pullers.

Alcaraz, the world number three and 2022 champion in New York, was stunned by Dutch world number 74 Botic van de Zandschulp 6-1, 7-5, 6-4.

Alcaraz had made at least the quarter-finals in his three previous appearances in New York. Thursday's defeat was his earliest at a Grand Slam since a second round exit at Wimbledon in 2021.

Defeat ended his dream of becoming only the third man in the modern era to win the French Open, Wimbledon and the US Open in the same season.

"The tennis schedule is so tight. I've been playing a lot of matches lately with Roland Garros, with Wimbledon, Olympic Games," said Alcaraz who lost a draining Olympics final to Novak Djokovic in Paris just over three weeks ago.

"I took a little break after the Olympic Games," he added. "Probably it wasn't enough. I came here with not as much energy as I thought that I was going to come. But I don't want to put that as excuse."

Meanwhile, orld number one Jannik Sinner, vying to add the US Open title to the Australian Open crown he won in January, breezed into the third round with a 6-4, 6-0, 6-2 victory over American Alex Michelsen.

Italy's Sinner needed just an hour and 39 minutes to get past the 49th-ranked Michelsen, giving himself a match point with a crisp forehand winner down the line and polishing it off with a crosscourt forehand volley.

"It was a real improvement, for sure," said the 23-year-old, who had to rally from a set and a break down in an unconvincing first-round win over Mackenzie McDonald.

"I'm looking to get better now in the next days," said the Italian, who hit the practice court shortly after the match "trying to understand what works here best on these courts."

"Let's see what I can do in the next round," added Sinner, who next plays Australian wild card Christopher O'Connell on Saturday. (AFP)