Andy Murray admitted his quarter-final victory over defending Australian Open champion Rafael Nadal had left him feeling hollow after the Spaniard was forced to retire due to injury.
The 22-year-old Scot was already firmly on track to claim one of the most memorable victories of his career when the world number two called an end to the contest trailing 6-3 7-6 (7/2) 3-0.
Nadal suffered the injury during the closing stages of the second set and soon after calling for a trainer early in the third the left-hander decided he could not go on.
It brought a premature end to a contest that had, until Nadal's injury, captivated a capacity 15,000 crowd at the Rod Laver Arena.
Murray produced arguably the best tennis of his career as he twice fought back from a break down in the opening two sets to claim them before Nadal pulled out.
"I'm obviously disappointed that the match couldn't have finished as I would have liked," the fifth seed said.
"But with the position I was in I feel like I would have had a chance of going on to finish the match.
"You know, unfortunately that happens sometimes in sport. A win's a win.
"It was a very good performance. I won the big moments in the match. I thought I dictated a lot of what happened on the court."
Murray admitted he had not expected Nadal to retire despite the Spaniard calling for the trainer.
"It just all happened so sudden," he said. "There was one backhand in the following game he didn't quite run for.
"I didn't realise it was such a big problem.
"I was very surprised because I've seen Rafa play matches where he's obviously been in a lot of pain and discomfort and he's played on. It's a shame."
Murray identified his ability to break back immediately in both sets after going behind as crucial in his win -especially in the second set after the players had been forced to take a 10-minute break during a fireworks display to celebrate Australia Day.
"The first time (I broke back) was good. The second time was a lot more important," said Murray, who revealed the players has been warned before the match that they would take a break for the fireworks display.
"That break (for the fireworks) it's the first time I really had to do something like that.
"It was pretty cold on the court, as well. I tweaked my back a little bit on the first point of that game. He mis-hit a return when I was serving and volleying.
"You just get a little bit stiff. It was big for me to get that break back."
Nadal apologised to Murray after the match for his decision to retire.
The Spaniard admitted he was already a beaten man at that point and said he decided not to go on to prevent suffering long-term damage after knee tendinitis undermined his second half of the 2009 season.
"I felt the pain at the end of the second set and I felt a similar thing to what I had last year," the 23-year-old said.
"After that I can't go down so it was impossible to win the match.
"When I have the chance to play I never retired. But anyway I knew I was going to lose. I said sorry to Andy for that."
Murray will now play 14th seed Marin Cilic in the last four as he looks to reach his second grand slam final.
Cilic beat the Scot in straight sets when they last met at the US Open in September, but after tonight's performance Nadal is backing Murray to go through to the final.
"Andy played really well I think. I think he's at an unbelievable level," he said.
"His serve was unbelievable. When I had my chances with the breakpoints he always served big.
"I just have to congratulate him because he's doing really well, and I think he has a big chance to win this tournament."