DOHA, Qatar — Top-ranked Rafael Nadal and Roger Federer won in straight sets to advance to the quarterfinals of the Qatar Open today.

Nadal defeated Karol Beck of Slovakia 6-1, 6-2, and Federer stopped Andreas Seppi of Italy 6-3, 6-3. Andy Murray defeated Philipp Petzschner 6-2, 6-4.

"I am happy because it was an important win," said Nadal, who took advantage of 27 unforced errors from Beck.

Federer was broken twice but managed to beat Seppi, who committed 31 unforced errors — two more than Federer.

Murray lost to Federer in the U.S. Open final. But unlike Nadal and Federer, Murray was not broken in the match.

"My first serve percentage was good," Murray said. "I know he uses a lot of backhand slice shots, so I was able to keep my shots hard and flat. I think it was a good match for this stage of the tournament."

Nadal, who won the French Open and Wimbledon last year, said it's too early to predict the level of his game.

"I can't say if I am close to my best," he said. "You can never tell whether you are at your best."

Nadal will play fifth-seeded Gael Monfils of France in the quarterfinals on Thursday.