Rafael Nadal seized Roger Federer's ATP number-one ranking with a victory over Nicolas Lapentti 7-6 (7-3), 6- 1 in a Friday quarter-final at the Cincinnati Masters.

Nadal clinched the promotion no later than August 18. If he can win the title on Sunday at the Ohio tournament, he can claim the top spot immediately on Monday, a week before the start of the Beijing Olympics.

"I'm so happy to be getting number one," said Nadal. "I was also happy to be number two. I won a lot of matches. It's been tough. I have a lot of matches on my back."

The Spaniard, holder of five Grand Slam titles including Paris and Wimbledon this season over Federer, noted the tough conditions due to the heat in Cincinnati.

"I fought hard to get here," Nadal said. "It's tough to play well after winning Toronto last week."

Lapentti, ranked 89th, had reached the top 10 nearly in 1999 but has fallen off the map. He played in his last Masters quarter-final in 2002 in Miami.

Federer, atop the table for four and a half years, was beaten in the third round by Croatian Ivo Karlovic to open the door for Nadal's final rise to the top.

Nadal will have to recover in time for a semi-final battle against Novak Djokovic, against whom he stands 9-3 with three consecutive wins this season.

Djokovic knocked off Ernests Gulbis 6-3, 6-4 to produce his second win since May over his childhood tennis companion.

Djokovic, seeded third, stopped the teenager from Latvia in the French Open quarter-finals as the friends from the Niki Pilic academy in Munich begin playing each other at the top level.

Ivo Karlovic hit 24 aces in his quarter-final win over German Philipp Kohlschreiber 7-6 (8-6), 7-6 (7-3).

The 16th seed will take on Andy Murray, who reversed his form in dramatic fashion to reach a second straight Masters semi-final with a win over former champion Carlos Moya 2-6, 6-3, 6-1.

Djokovic, a quarter-final loser to Murray a week ago in Toronto, lavished praise on fast-rising Gulbis.

"I've known him a long time. He's very talented and coming up, a rising star," said the 21-year-old Serb. "He's a very powerful player. I knew I'd have to be consistent in order to win."

Djokovic needed a break per set to advance against the 19-year- old. Murray looked like he would melt in the mid-30s Celsius heat on court in the torrid Midwest, before he rallied to prevent a disaster against Moya, Spain's former world number one and 2002 winner.

Murray will compete in the fifth Masters semi of his career, having never gotten past that stage.

"It was really tough at the start," he said. "I've never been to the final of a Masters, but this looks like my best chance. I'm playing well enough and can hopefully come through."