Madrid - Rafael Nadal saved two break points in the final game to earn a victory over Feliciano Lopez on Friday at the Madrid Masters, with the top seed advancing 6-4, 6-4 to join Roger Federer and Andy Murray in the semi-finals.

Nadal, the 2005 champion who exited in the quarter-finals in the last two editions, said that he was relieved to get through after taking heavy treatment on his shoulder until just before the start of the match.

"It was touch and go," said the top seed, who faces a semi-final on Saturday against France's Gilles Simon, who overcame 27 aces from Croatian serving machine Ivo Karlovic 7-6 (7-1), 4-6, 7-6 (7-2).

Roger Federer and Andy Murray will duel for the third time this season after the Swiss second seed hammered Argentine Juan Del Potro 6-3, 6-3.

Federer joined Murray, who beat France's Gael Monfils 6-2, 6-2 in lining up a repeat of the US Open final six weeks ago.

The Swiss is showing devastating form after taking a three-week break from the game, returning only at the last minute to enter Madrid. He and Murray stand level at two wins each in their series.

"I'm happy to be playing again. I've played well so far," said the 13-time Grand Slam champion. "I've not been broken and played well in key moments. I'm putting on pressure and creating chances."

Murray called his effort over Monfils one of his best matches this season. The 21-year-old number four hopes that he can take his chances against Federer when they meet again.

"I'm pretty relaxed just now. I've qualified for the Masters Cup, and I just want to play some matches," Murray said.

"I've been playing great in practice, and hopefully I can keep doing it in matches. I'm not putting a whole lump of pressure on myself to win every time."

Nadal stands 4-1 over Lopez, losing their first encounter in 2003 but posting wins ever since. The Spanish top seed said that playing his friend was tough.

"We know each other and each other's game so well," said Nadal, the reigning Roland Garros, Wimbledon and Olympic champion. "It's always tough to play him. I tried to play aggressive with my backhand slice."

Nadal owns an impressive eight titles in 2008 but would love to claim more success, after taking over the number one spot from Federer for the first time earlier this season. According to ATP calculations, if he reaches the final, Nadal will take the top standing for the rest of 2008.

Federer won his third match against Del Potro, who broke through with four straight tournament titles over the summer.

"He started off serving great with many aces," said Federer. "Before, his serve was his weakness. That's a change in his game. But I know I can stay calm and wait for my chances. I'll always hang in."