MELBOURNE, Australia — Andy Murray had been warned about the fireworks, the crackle and dazzling burst of color that lights the sky to mark Australia Day celebrations.

So the pyrotechnics came as no surprise in the second set against defending champion Rafael Nadal. What he didn't expect was the fizzle at the end.

Nadal quit their quarterfinal while trailing 6-3, 7-6 (2), 3-0 Tuesday night, not long after he'd taken a medical timeout to treat his right knee. His concession came five games and a tiebreaker after he tripped and fell following the fireworks delay at Rod Laver Arena.

Andy Roddick also needed a medical timeout — after the first set of his earlier match against No. 14 Marin Cilic. His sore right shoulder was making his fingers numb.

Roddick played on for another four sets. But, like Nadal, he was gone in the quarterfinals. Cilic advanced 7-6 (4), 6-3, 3-6, 2-6, 6-3 and will meet Murray in the semifinals.

Murray was convinced he would have beaten Nadal even if the match had gone the distance. He's also confident of overturning his last result against Cilic — a loss at the U.S. Open — and reaching his second Grand Slam final.

"When the big moments came in the match, I thought I dictated what happened," Murray said. "From my side, I played really well and deserved to be up when the match was stopped."

Nadal tweaked his knee in the 11th game of a second set that had already been interrupted for nine minutes by fireworks. Both players had been told in advance about the break, although both took time to readjust to match conditions.

Nadal's fall six games later sent a murmur around the stadium, but he eased concern by playing a shot by instinct as he sat near the baseline. Murray won that point, but Nadal held serve in the game and celebrated with a flurry of wild, double-arm pumps as if he'd won a final.

He didn't show any outward signs of being hurt until calling for a medical timeout while serving at 0-1 and 15-all in the third set. He took a three-minute break while the trainer worked on his right knee. He played only 13 more points before walking to the net and shaking Murray's hand.

Nadal said he didn't want to risk long-term damage. Knee tendinitis sidelined him for long periods last season, preventing him from defending his Wimbledon title.

"Is not a lot of history because was during the match ... in the end of the second set in one drop," Nadal said. "And I felt similar thing to what I had last year.

"After that I can't go on ... was impossible to win the match. So I said, 'Well, no repeat the same mistake like I had last year.' I go to the limit, but not cross the limit, no?"

Nadal held off fellow Spaniard Fernando Verdasco in a five-set semifinal last year that was the longest match in the tournament's history before beating Roger Federer in five sets in the final.

Federer is still in the equation this year at Melbourne Park, where he is aiming for a fourth Australian title and a 16th Grand Slam crown.

He plays Nikolay Davydenko in the quarterfinals Wednesday and is on a two-match losing streak against the Russian after winning their first dozen head-to-heads.

The winner of that match will play the victor of 2008 champion Novak Djokovic vs. Jo-Wilfried Tsonga — a rematch of the final from two years ago.

Serena and Venus Williams need wins Wednesday to set up a sisters semifinal: Four-time champion and No. 1-ranked Serena faces No. 7 Victoria Azarenka and sixth-seeded Venus takes on China's Li Na.

Former No. 1 Justine Henin resumed her strong comeback by beating Nadia Petrova 7-6 (3), 7-5 to reach the semifinals. She next plays 2008 Wimbledon semifinalist Zheng Jie, who beat Maria Kirilenko 6-1, 6-3 in the other quarterfinal.

Henin quit in May 2008 while holding the No. 1 ranking. She is now playing as a wild card and is two wins from becoming the second Belgian in as many Grand Slam tournaments to win in her comeback from retirement. Kim Clijsters won the U.S. Open in September after two years off to get married and have a baby.

Roddick took off the end of last season to recover from a knee injury. Now he's got a shoulder to worry about.

The 27-year-old Roddick has lost four Grand Slam finals, including last year's five-set Wimbledon thriller against Federer, since winning his only major at the 2003 U.S. Open. The time between then and now represents the longest title drought for American men in Grand Slam singles.

The wait has been much longer for Britain, which hasn't had a men's major winner since Fred Perry in 1936. Nadal predicted Murray could end the wait by winning this title.

"For Andy, I think he deserves to win his first Grand Slam," Nadal said. "And I think he's going to do it.

"There's a very good chance for him. First thing, he's playing very well. Second thing, he's already in the semifinals. He's only two matches away."

At the same time, Nadal isn't writing off his own chances of contending again at the Grand Slams. He hasn't reached another final since he won his first hardcourt major in Melbourne last year.

And he's had to remodel his game to incorporate more big hitting and less running, to limit the wear and tear on his knees.

He didn't even want to discuss his future Tuesday night.                

"Don't start, guys, with these questions right now. I think is not the right moment," he said. "Today I played against one of the best players of the world, and I think I wasn't run more than him.

"I played aggressive. I played having control of the point, a lot of the time with the forehand and the backhand, too, returning aggressive. If you see my matches three years ago, that didn't happen, no?"

As for the knees?

"Well, I worked a lot. I didn't have lot of problems for the last six months. And today is the first," recurrence, he said. "I felt something when I think is a bad movement. But is not because the knee is tired. No, I think going to be OK."