Third seed Jelena Jankovic outfought defending champion Serena Williams in an enthralling match to win 6-3 6-4 and reach the Australian Open semi-finals.
Jankovic will play Maria Sharapova for a place in the final
With Williams restricted by a huge blister, Jankovic recovered from a poor start to run away with the first set.
Jankovic's thigh was also proving troublesome and both players needed lengthy treatment in the second set.
Williams initially raised her game when the match restarted but it was Jankovic who dug deepest in the end to triumph.
"In the second set I felt a sharp pain in my quad, and it was like a knife went in my leg. It was really painful," Jankovic said.
"I thought, 'Oh, my God, again, another one? I'm kind of sick of all these injuries'.
"But I'm like a wounded animal, I still keep going.
"The most important thing is that I fight on the court, and I always give my best and I never give up - those are the qualities that got me through the semi-final."
Williams, who later would lose a women's doubles quarter-final with her sister Venus, said: "I had some issues but I don't like to make excuses,"
"I definitely had a problem all through the day, but nothing life-threatening, so it's fine.
"My shots were spraying and everything like that but definitely Jelena played some great tennis and deserved it.
"I felt I was gonna do better than this but I guess I was wrong... you can't always be right."
The Serbian will play the 2007 runner-up Maria Sharapova in the semi-finals after the Russian thrashed Justine Henin 6-4 6-0.
It was an unbelievable match - I am still shaking
When Williams beat Sharapova to win her third Australian title 12 months ago, she breezed past Jankovic in the fourth round.
And, briefly, a similar outcome seemed probable when the seventh seed easily broke the Serb to move 2-0 ahead in the first set.
Jankovic had come into the match nursing a bad back, knee and shoulder, not to mention the baggage of some hard-fought victories earlier in the tournament.
And such was the ease with which Williams moved clear, you feared those battles were beginning to take their toll.
Instead, it was the American who began to falter, with her usually formidable serve non-existent and proving as much of a handicap as her puzzling inability to move freely around the court.
Jankovic did not stop to wonder why her opponent was playing so poorly and took eight of the next nine games, clinching the first set without meeting much opposition.
A large blister left Serena Williams in pain throughout the match
Only in the second set, when Williams gingerly removed her right sock to reveal her painful big toe, was the source of her discomfort clear.
But by this stage Jankovic was also in trouble with her left thigh and the match was held up for several minutes while both players received treatment.
When they eventually resumed, the next game saw Williams save four break points before moving level at 3-3 and you sensed that she still had it within herself to save this match.
However, she again pressed the self-destruct button rather than pushing forward, wasting a chance to break Jankovic before seeing her own serve falter again.
That left Jankovic serving for the match but there was still time for one last effort by the champion, who produced some astounding returns to keep her hopes alive.
The crowd were willing Williams on but sadly her inconsistency proved decisive in the next game, as two big serves were followed by two double-faults and a wide forehand that allowed the world number four to close out a dramatic victory.
"It was an unbelievable match," Jankovic said. "I am still shaking.
"It's amazing to beat the defending champion and a champion like Serena, it doesn't happen every day."
"Getting revenge for last year feels so good and I am so happy to be in the semi-final, having no expectations, having injuries, and not really thinking that I can go far."