In a tournament where outfits have drawn attention in both the men's and women's draws, Alcaraz's loose-fitting brown Nike tank top, a Travis Scott x Cactus Jack collaboration, kept slipping to expose his chest.
The seven-time Grand Slam champion's outfit prompted plenty of memes and witty comments online, with former WTA Tour player Eugenie Bouchard jokingly telling him to "put the nip away."
For his third-round match with China's Wu Yibing on Friday, Alcaraz stepped onto Arthur Ashe Stadium wearing a white undershirt beneath his kit.
"I think I've been seeing too much of my nipples lately," Alcaraz told reporters with a laugh after his 6-3 6-4 6-1 win.
The 23-year-old confirmed that the decision to add the undershirt was entirely his own.
"I feel really comfortable with another shirt. So I think I'm going to stay like that," he added.
Alcaraz, who is returning from more than four months out with a wrist injury, has lost one set through his first three singles matches at Flushing Meadows. He next faces American 20th seed Tommy Paul, an opponent he has beaten five times in a row.
"He's a really talented player, really difficult one to play," Alcaraz said. "I think he's really dangerous for everyone on the tour. I'm really looking forward to playing him once again."