Roger Federer, the top-ranked men's tennis player in the world, wipes his face during a changeover in a second-round match with Andy Murray at the Western & Southern Financial Group Masters Wednesday in Mason, Ohio. Murray upset Federer, 7-5, 6-4.

MASON, Ohio — Exasperated with another errant shot, Roger Federer swatted the fuzzy, yellow ball up and over the blue bleachers in the corner of the stadium, sending a murmur through the crowd.

Tennis fans aren't used to seeing this from the world's best player.

A few minutes later, they watched him trudge to the net to shake the hand of a disbelieving teenager who had just pulled off a most unexpected upset, ending Federer's two years of dominating the continent.

Britain's Andy Murray ended Federer's 55-match winning streak in North America with a straight-set victory Wednesday in the Western & Southern Financial Group Masters, a second-round upset that stunned everyone except Federer himself.

"Obviously, I wasn't expecting to win today, so when it did happen, I was in a little bit of shock," the 19-year-old Murray said.

Federer had an explanation for his earliest tournament exit in two years: Too much tennis.

After he won a tournament in Toronto on Sunday, Federer had only one day to travel and get ready for Cincinnati, where he lost two years ago before starting that streak. He knew it was going to be tough to keep going.

"I knew that my expectations were not to win the tournament here," Federer said. "They were to survive a few rounds. So that's why I'm not disappointed after this loss. I expected kind of a result like this."

The Swiss star may have expected it, but he sure didn't like it.

Federer repeatedly mumbled to himself, dropped his head in frustration and made that out-of-the-stadium swat as his troubles mounted. Murray, in only his second season on the tour, broke Federer's serve seven times overall, including three times in a row in the first set.

Not bad for an up-and-comer who got a basic pep talk from his new coach, Brad Gilbert, before the match.

"He basically said to me the most important thing was to believe and think that you had a shot of winning going into the match," said Murray, ranked a career-best 21st in the world.

Taking advantage of Federer's unreliable serve and unresponsive backhand, Murray sent him to his first loss on the continent since Dominik Hrbaty beat him in the first round of the same tournament two years ago.