Carlos Alcaraz is through to the US Open second round after Argentine Sebastian Baez was forced to retire on Arthur Ashe Stadium.

Alcaraz, 19, is bidding to win his maiden Grand Slam title in New York.

He is also one of four players who could finish the tournament as the world's top-ranked men's player.

"Nobody wants to see the match end like this," said Alcaraz. "Sebastian is a great player and he deserves the best things.

"It was really tough, the second set was really tough for me to stay at the level physically and mentally, but the energy I received on Arthur Ashe was really special."

The Spaniard reached his first major quarter-final at last year's US Open - a feat he matched at the French Open in May.

He added: "Last year was one of the best moments of my life and of my career. One year later, being fourth in the world, is something special for me."

Having edged the first set by clinching the contest's first break of serve in the 12th game, Alcaraz maintained that momentum by striking early in the second.

A breathless second set featured several enthralling battles - with Baez breaking back in a 13-minute third game which had the crowd on their feet, before once again requiring a fifth break point to move 4-3 up.

But it was Alcaraz who finished stronger in humid conditions as the match passed the two-hour mark, claiming a fourth game in five as he eventually took a fourth set point on his opponent's serve.

Baez required a medical timeout before starting the third set and it was soon clear he would not be able to be competitive, taking the decision to retire after falling a break down.

Elsewhere in the men's draw, Bulgarian 17th seed Grigor Dimitrov beat American Steve Johnson 6-3 6-2 6-2.

He will face another American in Brandon Nakashima next, following the 21-year-old's 7-6 (7-4) 6-2 6-2 win over Russian Pavel Kotov.

Another home player, John Isner, won 6-3 6-1 7-5 against Argentine Federico Delbonis, while Frenchman Richard Gasquet defeated Japan's Taro Daniel 6-4 6-7 (1-7) 6-2 6-2.