NEW YORK -- Defending champion Rafael Nadal's only trace of a problem during his second-round victory at the US Open was a warning for letting the 25-second serve clock expire.
And Nadal was convinced that even that wasn't really his fault.
Nadal won 46 of 55 first-serve points and wore down Vasek Pospisil 6-3, 6-4, 6-2 in Arthur Ashe Stadium on Wednesday night.
The serve clocks are making their Grand Slam debut at Flushing Meadows, and folks have been curious to see whether that would have any effect on Nadal, who is known for taking his time between points. At 2-1 in the final set, he drew a warning from the chair umpire because the 25 seconds ran out. Nadal was convinced that the only reason that happened was that he paused when Pospisil briefly put a hand up to ask him to wait.
Either way, the two-hour win was over soon thereafter.
Earlier in the day, Andy Murray saw his return to the US Open end after just two rounds.
The 2012 champion was eliminated by No. 31 seed Fernando Verdasco 7-5, 2-6, 6-4, 6-4. The Spaniard will face a second straight past champion at Flushing Meadows when he meets third-seeded Juan Martin del Potro, the 2009 champion, in the third round.
Murray missed last year's tournament because of a hip injury and didn't consider himself a contender this year because of his lack of preparation.
Verdasco won for just the second time in 15 career meetings with Murray, who had multiple chances to even the final game of a 64-minute final set before the left-hander finished it.
"I think some of the tennis I played today was some of the best I've played since I had the surgery or since I came back," Murray said. "But there were also periods in the match, especially in the first set, where, you know, I really didn't play particularly well. I hit a lot of mistakes when I was up in that set. I feel like I should have won the first set and didn't.
"Then kind of at the end when back was against the wall, I came up with some good tennis to make it close and interesting at the end and almost got myself back into it. You know, there were too many ups and downs for my liking."
Del Potro, the 2009 winner, beat American Denis Kudla 6-3, 6-1, 7-6 (4).
Wawrinka, the 2016 champion who missed the Grand Slam tournament last year because of two left knee surgeries, won 7-6 (5), 4-6, 6-3, 7-5. The unseeded Swiss next faces No. 25 seed Milos Raonic of Canada in the third round.
Raonic swept past Gilles Simon of France 6-3, 6-4, 6-4.
The 11th-seeded Isner is the highest-ranked American man in New York for the seventh time in a row, but he has only once made it to the fourth round in that span.
He broke Jarry for the second and last time at 4-all in the fifth set, flicking a backhand lob winner to take that game.
After serving out the win, Isner walked over and slapped palms with front-row spectators.
Sock, a 25-year-old American, ended a seven-match main-draw losing streak by winning in the first round. But his loss to the 37th-ranked Basilashvili means Sock still has not won two consecutive matches all year.
Sock's record for 2018 is 6-16.
It was a surprisingly early exit for the 20-year-old Greek after his strong hard-court season. He had 64 unforced errors against just 27 winners in the match that lasted 2 hours, 48 minutes.
Tsitsipas beat four top-10 opponents in Toronto -- becoming the youngest player to do so at an event since the ATP World Tour began in 1990 -- before losing to Nadal in the final. He also reached the semifinals in Washington and came into the US Open as the highest-seeded debutant since Richard Gasquet was No. 13 in 2005.
The Associated Press contributed to this report.