Rafael Nadal's bid at record 21st Grand Slam over, upset by Stefanos Tsitsipas

Stefanos Tsitsipas has upset Rafael Nadal at the Australian Open, ending the Spaniard's chances of winning a record 21st Grand Slam title.

Stefanos Tsitsipas reacts after winning the ATP World Finals singles final Source: Associated Press

The Greek fifth seed made it into the semi-finals in Melbourne after an epic performance where he came back from two sets down against Nadal.

The World no. 2 had not lost a set coming into the clash, but quickly saw his lead eaten up by Tsitsipas, who out gunned Nadal 3-6 2-6 7-6(4) 6-4 7-5 to complete an epic comeback.

"I'm speechless, I have no words to describe what just happened on court," said Tsitsipas, who was still out of breath in his on-court interview.

"My tennis speaks for itself. It is an unbelievable feeling to fight at such a level and give it my all on the court.

"I started very nervous, I won't lie. I don't know what happened after the third set. I flew like a little bird.

"Everything worked for me and the feelings are indescribable."

The 34-year-old Spaniard was naturally disappointed, his record bid in Melbourne imploded so spectacularly.

"Of course, [I'm] sad. I lost a match in quarter-finals of an event that means a lot to me," Nadal told reporters.

"I tried my best in every single moment. I think I stayed positive all the time during the match, fighting, and it was not enough. Sometimes it's enough, today was not enough."

Tsitsipas will face Danill Medvedev in the final four, after the Russian's straight sets win over Andrey Rublev.