Spanish teenager Carlos Alcaraz battled into the US Open second round on Tuesday when Argentine opponent Sebastian Baez retired injured.
Alcaraz, a quarter-finalist in New York in 2021, won through 7-5, 7-5, 2-0 in two hours and 31 minutes on Arthur Ashe Stadium.
"Nobody wants to see a match end like this. Sebastian is a great player, fights to the last ball and deserves better things," said the 19-year-old.
After a gruelling 83-minute second set, world number 37 Baez called the trainer for a medical timeout but gave up the fight two games into the third set.
"Last year was one of the best moments of my life," said Alcaraz who reached the last eight in New York with a ranking of 54.
"It's a such a special place for me to play on the biggest stadium in our sport."
Alcaraz will face either Tallon Griekspoor of the Netherlands of Argentina's Federico Coria for a place in the last 32.