NEW YORK -- Any time now, Andy Murray will break through and become Britain's next Grand Slam champion.

Or so the theory goes.

Andy Murray felt the sting of a second straight early departure from the U.S. Open, losing in the third round Sunday. Stan Honda/AFP/Getty Images

The fourth-seeded Murray, expected by many to make a deep run at this year's U.S. Open, instead made his second straight earlier-than-expected exit from Flushing Meadows -- losing to No. 25 Stanislas Wawrinka on Sunday in the third round.

Wawrinka rallied from a break down late in the second set for a 6-7 (3), 7-6 (4), 6-3, 6-3 upset -- a loss certain to be picked apart by the tennis-loving fans back home.

"I have no idea of whether I'll win a Grand Slam or not," Murray said. "I want to. But if I never win one, then what? If I give 100 percent, try my best, physically work as hard as I can, practice as much as I can, then that's all I can do."

Murray is trying to become the first British man to win a Grand Slam tournament since 1936. He was a popular pick this year, based on trips to the finals at Flushing Meadows two years ago and this year's Australian Open, along with a championship in Montreal last month in which he beat both Rafael Nadal and Roger Federer.

Wawrinka's upset was the only significant surprise on a day that saw the top-seeded Nadal and four other Spaniards advance: No. 8 Fernando Verdasco, No. 10 David Ferrer, No. 23 Feliciano Lopez, and unseeded Tommy Robredo.

"Probably the most difficult tournament for us, no?" Nadal said after beating Gilles Simon of France 6-4, 6-4, 6-2. "So that is very important news for Spanish tennis."

Murray alone bears the burden of Britain's hopes for its first male Grand Slam champion since 1936. He was a popular pick to go far at Flushing Meadows; he was the runner-up at the 2008 U.S. Open and at this year's Australian Open, also on hard courts.

The promise of a deep run this year for Murray slipped away quickly after the second set. The 23-year-old Scot needed the trainer twice after that -- once for tightness in his quad, another when he felt tingling in his right elbow.

But he didn't blame the injuries.