DUBAI, United Arab Emirates (AP) — Australian Open champion Novak Djokovic remained unbeaten this year by routing Andreas Seppi of Italy 6-0, 6-3 as the top four seeds powered into the semifinals of the Dubai Championships on Thursday.

Defending champion Roger Federer defeated Nikolay Davydenko 6-2, 6-2.

Djokovic will play fourth-seeded Juan Martin del Potro, who returned to the semifinals by beating German qualifier Daniel Brands 6-4, 6-2. Federer will face third-seeded Tomas Berdych, who defeated Russian wild card Dmitry Tursunov for the second time in five days, 6-3, 6-2.

The top-ranked Djokovic won his 11th straight match to start the year. He broke three times in the first set and once in the second, which was a little more competitive. But a strong first serve — he won 89 percent of points on it — and a powerful forehand helped him improve to 10-0 against Seppi.

"It was an even better performance than first two matches, so match after match I'm elevating the level, which is good," Djokovic said. "I'm trying to do my best on the court. Tomorrow I have a big challenge, the biggest so far. Hopefully I can sustain the level from today."

Federer also had little problem with Davydenko, breaking him twice in the first set. The second set was much the same, as Federer jumped out to a 4-1 lead. Federer had two aces and an overhead smash to make it 5-1 and served it out at love.

Federer said he expected a much bigger challenge from Berdych, who beat him at the U.S. Open.

"He's got amazing power, one of the strongest guys out there on tour," Federer said. "I've struggled somewhat against him, but very often it's because his game is so big that, you know, he has a big say in the outcome of the match."

Del Potro managed to neutralize the big-serving Brands and said his right wrist, which he injured in 2010, was not bothering him as much as it did earlier in the tournament.

"I served well today. I didn't (concede) any break points. I think I took all my chances to break his serve," del Potro said.

Del Potro knows he'll need to be healthy against Djokovic.

"The good thing is I'm not getting worse. It's a good thing to be 100 percent," he said. "I know against Djokovic tomorrow I need to hit my backhand 100 percent and then see if I have a little chance to win."

Berdych also served well against Tursunov, hitting nine aces and winning 81 percent of points on his first serve. He moved the Russian around the court, aware that Tursunov's sore left hamstring limited his mobility.