Second seed Nadal was on course for a comfortable victory before Tsitsipas turned the match around to prevail 3-6, 2-6, 7-6 (7/4), 6-4, 7-5 in a seismic upset
Greece's Stefanos Tsitsipas recovered from two sets down to stun Rafael Nadal in the Australian Open quarter-finals on Wednesday, ending the Spaniard's bid for a record 21st Grand Slam title.
Second seed Nadal was on course for a comfortable victory before Tsitsipas turned the match around to prevail 3-6, 2-6, 7-6 (7/4), 6-4, 7-5 in a seismic upset.
"I don't know what happened after the third set -- I fly like little bird, everything was working for me," Tsitsipas said.
"The emotions at the end were indescribable, they were something else."
It was just the second time Nadal had lost when two sets up in a Grand Slam, having previously fallen to Fabio Fognini in the third round of the 2015 US Open.
Nadal, 34, remains tied with Roger Federer on 20 Grand Slam titles, but Novak Djokovic can pull within two if he wins his 18th major trophy at Melbourne Park.
Fifth seed Tsitsipas will now attempt to reach a maiden Grand Slam final when he plays the in-form Daniil Medvedev in the semi-final.
He beat Nadal for just the second time from eight matches. Djokovic will play the other semi-final against Russian qualifier Aslan Karatsev.