An exhausted Murray rallied on aching legs in the third set Thursday, beating American Robby Ginepri to reach the quarter-finals of the Western & Southern Financial Group Masters.

One day after he ended Roger Federer's two-year run of 55 straight victories on the continent, the 19-year-old Murray added to a modest run of wins that has marked him as an up-and-coming player.

Beating the world's top-ranked player was stunning. So was this win, for a different reason.

``That was the most tired I've been on a tennis court before,'' said Murray, eating a peanut butter sandwich to replenish his energy. ``I wasn't feeling well. At the end of the match, I wasn't thinking what I was doing in points. I was just trying to get the ball on the court.''

He could barely shuffle to the net after Ginepri's short backhand return finished off the 7-6 (3), 2-6, 6-4 win. Like Federer, Ginepri had backed Murray into a corner several times during the 2-hour, 6-minute match, only to watch him escape.

``It was obvious to everyone he was exhausted out there,'' Ginepri said, trying to comprehend how he'd lost. ``That match was just in the palm for the taking. I let it go by like that. I started playing a little bit tentative.''

Murray's next opponent will be Andy Roddick, who beat Argentina's Juan Ignacio Chela 6-3, 6-4. The quarter-final match is scheduled for Friday night, giving Murray a few extra hours to recover.

``He's been as good as anybody the last couple of weeks,'' said Roddick, playing his first tournament since he strained his left side in July. ``His draw here hasn't been easy.''

Murray has won 20 of his last 25 matches, reaching the finals at Washington, the semifinals in Toronto and now the quarter-finals in Cincinnati. In only his second year on the tour, Murray has risen to No. 21 in the world rankings.

All the tennis of the last few weeks caught up with him.

``That's 13 matches in 16 days. I'm not used to it,'' Murray said. ``My legs today just weren't there. I felt it early on. My first step wasn't fast. My legs were burning after each point.''

Ginepri was much fresher and appeared to be in control after Murray lost his energy and the last eight points of the second set. Up 4-3 in the final set, Ginepri couldn't finish him off. Murray broke him back, then found one final burst of energy.

``When you get to 4-all in the third set, regardless of how tired you are, you see the finish line,'' Murray said.

While Murray pulled off another surprise, No. 2 seed Rafael Nadal continued to play better as he gets deeper into the tournament, beating No. 14 Tommy Haas 7-6 (5), 6-3 to reach the quarter-finals.

Nadal lost in the third round at Toronto last week, and needed three sets to get past Sam Querrey in his opening match in Cincinnati. He's been much sharper the last two days.

``I feel comfortable on court,'' Nadal said. ``I was playing my best tennis in the first games.''

His next opponent is fellow Spaniard Juan Carlos Ferrero, who beat Robin Soderling 7-5, 6-4. Nadal has won five tournaments this year, two fewer than Federer. He lost to Federer in four sets for the Wimbledon title, and is rounding into form with the U.S. Open at hand.

Haas provided a good test, having won 14 of his last 18 matches. He needed treatment for a blister on his foot during the first set and again after he dropped the tiebreaker.

``He's very quick, gets a lot of balls back, and once in a while he does some phenomenal shots,'' said Haas, who had never played him. ``When you think actually you're going to get an easy ball back, he seems to come up with an incredible winner or passing shot.''

No. 4 Ivan Ljubicic beat No. 16 Dominik Hrbaty 7-5, 6-4, extending his run of playing deep into tournaments. Ljubicic has reached the quarter-finals in 10 of his 13 tournaments this year, compiling a 49-13 match record. He'll play Spain's Tommy Robredo, who beat France's Florent Serra 6-3, 6-1.

In the other quarter-final match, No. 13 Fernando Gonzalez will play No. 10 David Ferrer, the fourth Spaniard still in the tournament.