* Injured Nadal exits
* Murray reaches semi-finals
* Clijsters, Zvonareva set up semi (writes through after Nadal exit)
Rafa Nadal's dream of winning four grand slam titles in a row ended with a whimper on Wednesday when his body failed him at the quarter-final stage of the Australian Open for the second successive year.
The record books will show the 24-year-old lost 6-4 6-2 6-3 to fellow Spaniard David Ferrer on Rod Laver Arena but the injury the world number one suffered in the third game rendered the match a no contest for most of its 153-minute duration.
A rather apologetic Ferrer advanced to only his second grand slam semi-final where he will face British world number five Andy Murray who ended the run of Ukraine's Alexandr Dolgopolov, albeit not without some tricky moments.
Kim Clijsters remains favourite to win her first Australian Open after beating Poland's Agnieszka Radwanska 6-3 7-6 although Russia's Vera Zvonareva, hunting a first major, will provide a tough semi-final opponent after she beat Petra Kvitova 6-2 6-4.
Clearly hampered by what looked like a hamstring injury and with tears welling in his eyes at one stage, top seed Nadal still displayed champion qualities by refusing to retire when he was cannon-fodder for Ferrer.
"I hate retiring," he told reporters -- declining to go into detail about what had gone wrong.
"I can say nothing about the injury," Nadal said. "First of all, I don't know nothing. Second thing, for respect to the winner and to a friend, I prefer to talk about the match.
"It's a difficult day for me. I lost in quarter-finals another time. So I tried my best. I couldn't do more."
Nadal had not lost a grand slam match since hobbling out of Melbourne Park when his knees gave up on him in his last eight contest against Murray a year ago to the day.
The Mallorcan stormed back from that disappointment to win the French Open, Wimbledon and U.S. Open titles and returned to Australia with an eye on matching Don Budge (1938) and Rod Laver (1962, 1969) in holding all four major titles at once.
"In a tennis career, you have higher moments and lower moments," the nine-times grand slam champion said. "I have had almost all the time very, very happy moments and very nice moments in my career.
"It's part of the sport. Accept, keep working, try my best in the next tournament. That's what I can do."
Ferrer said he did not consider it a real victory.
"It was not easy because Rafa is a gentleman and he played with an injury as we are friendly," said the seventh seed, who reached his second grand slam semi-final and the first since the 2007 U.S. Open when he beat Nadal in the last 16.
"I fought a lot but for him with the injury it was not easy."
Murray, who lost the final here last year and would have been gearing up for a Nadal semi, was shaken but not stirred by swashbuckling Melbourne Park debutant Dolgopolov as he came though a tricky test 7-5 6-3 6-7 6-3.
Murray, who counts James Bond actor and fellow Scot Sean Connery among his fans, had been in intimidating form all week and continued in similar fashion to race to two sets and a break up against the "hit or miss" Dolgopolov.
The world number 46, however, suddenly found the touch and consistency that saw him upset Robin Soderling in the fourth round to break back and force a third set tiebreak, which Murray conspired to lose 7-3 with a string of errors.
Dolgopolov could not keep up the pace, though, and Murray won 14 points in a row at the start of the fourth set which sped by in 32 minutes as he kept alive his hopes of ending Britain's 75-year wait for a men's grand slam champion.
"I played well," said Murray. "I wouldn't say I was necessarily in trouble at any stage. I was ahead in most of the sets. But I thought I dealt with his game well."
In the absence of injured 2010 champion Serena Williams, Clijsters is the woman to beat in Melbourne.
The 27-year-old Belgian's game was far from perfect but she hustled and bustled her way through the opening set in less than half an hour and fended off a Radwanska fightback to secure the second, and the match, in a tiebreak.
"I just physically felt a little bit tired and heavy out there today," Clijsters said.
The three-times U.S. Open champion will probably have to raise her game for the semi-final against Zvonareva, who wore a black ribbon on her visor in memory of the victims of Monday's bombing at Moscow airport in her victory over Czech Kvitova.
An aggressive Zvonareva clipped through the first set in 29 minutes and was 3-0 up in the second when she also had a second set wobble before battling back to go through a comfortable winner when Kvitova overcooked a forehand after 75 minutes.
"There will be moments where you lose your focus and you will have one or two unforced errors," said Zvonareva, a tearful losing finalist at Wimbledon and the U.S. Open last year.
"But I'm really happy the way I handled the situation after, and I was able to come up with some good shots when I needed it and finish in two sets."