DUBAI, United Arab Emirates — Andy Roddick used his strong serve to upset Rafael Nadal 7-6 (5), 6-2 Thursday and reach the semifinals of the Dubai Tennis Championships, and then announced he has split with coach Jimmy Connors.

Roddick said that Connors resigned about a week ago because he wanted to spend more time with his family.

"I still have the utmost respect for Jimmy and thank him for his time," Roddick said.

He credited the eight-time Grand Slam champion for having greatly improved his backhand and boosted his "fighting spirit."

The sixth-ranked Roddick closed the match with one of his 17 aces, and had numerous service winners against the second-ranked Spaniard. One ace was 149.75 mph, breaking the Dubai serve record he set a day earlier.

"I knew I was going to hit it well, from the first point. I kind of let it fly, and that's what it took tonight," Roddick said. "Anything less than that and I wasn't going to win."

Roddick had several love games in the match, using his powerful forehand to keep Nadal at bay.

"The way he was serving tonight, it's tough," Nadal said. "You feel a lot of pressure when you're serving."

Nadal said he made too many errors on his forehands on crucial points.

"Against a big server you have to put these balls in if you want to win," Nadal said. "It's disappointing for me today."

Roddick will next face third-ranked Novak Djokovic, who beat Igor Andreev 6-2, 6-1.

"It's going to be a big challenge for both of us," Djokovic said. "Roddick has the strongest and probably the best serve in today's tennis."

Also on Thursday, Nikolay Davydenko edged Andy Murray 7-5, 6-4 to reach the semifinals. Murray, who had upset top-ranked Roger Federer in the first round, was forced out of his defensive game by the fifth-ranked Russian's hard serves and quick moves on the baseline.