Defending champion Rafa Nadal has advanced to the second round of the US Open after fellow Spaniard David Ferrer retired during the second set of their night match due to a calf injury.
World No.1 Nadal breezed through the first set without facing a break point but the 36-year-old Ferrer fought back in the second, breaking Nadal twice before the injury forced him to call it quits with the score at 6-3 3-4.
Ferrer, whose decision brought the curtain down on his final appearance at a grand slam, said he had taken an injection before the match but was in obvious discomfort and needed treatment before he pulled the pin.
"I'm so sorry because I can't finish the match, but anyway, thanks a lot," he said in a courtside interview.
Nadal paid tribute to Ferrer, whom he beat in the 2013 French Open final.
"I'm very sorry for him. He's one of my closest friends on the tour and we faced many amazing moments together," Nadal said.
"It's sad for him to finish like this."
Argentine 2009 champion Juan Martin del Potro, the third seed, had no trouble dismissing American qualifier Donald Young 6-0 6-3 6-4 in another evening fixture.
The day's action on Arthur Ashe Stadium began with Swiss wildcard Stan Wawrinka conjuring up some of his old Flushing Meadows magic to sweep past eighth-seeded Bulgarian Grigor Dimitrov 6-3 6-2 7-5.
After winning the US Open in 2016 Wawrinka was unable to defend his title last year after two surgeries on his left knee.
But the Swiss, 101st in the world rankings, looked right at home on a steamy Monday as he opened his account with a ruthless performance against one of the title contenders.
"I'm improving day by day," Wawrinka said.
"I'm improving tournament after tournament, match after match.
"And I can see that the last tournaments, it went really high, from struggling in the match, to competing at really high level.
"So I'm really happy with that."
South African fifth seed Kevin Anderson, last year's finalist, rallied to outlast Ryan Harrison 7-6 (7-4) 5-7 4-6 6-3 6-4 in a four hour and 14 minute slugfest while Austrian ninth seed Dominic Thiem accounted for Mirza Basic 6-3 6-1 6-4.
Other opening day winners in the men's draw were seeded Americans John Isner and Jack Sock, Canadian seeds Milos Raonic and Denis Shapovalov, Greek 15th seed Stefanos Tsitsipas, Croatian 20th seed Borna Coric and veteran Spanish 31st seed Fernando Verdasco.
