Russia's second seed Daniil Medvedev staged a stirring comeback from two sets down Wednesday to reel in Canadian 21-year-old Felix Auger-Aliassime and claw his way into the last four at the Australian Open.

Medvedev looked out for the count as ninth seed Auger-Aliassime held match point in the fourth set, but the world number two battled back to win 6-7 (4/7), 3-6, 7-6 (7/2), 7-5, 6-4 and he will now play Stefanos Tsitsipas in Friday's semi-finals.

Medvedev had beaten Auger-Aliassime in straight sets in their US Open semi-final last September, but the roles were dramatically reversed in their return Grand Slam bout in Melbourne.

The Russian was looking down the barrel of a stunning defeat and was down a match point before he turned around the momentum winning a third set tiebreak to edge home against the determined Canadian and cap a grand comeback.

"I was not playing my best and Felix was playing unbelievable, he was all over me to be honest, I didn't know what to do so I said to myself 'what would Novak (Djokovic) do'," Medvedev said, referring to the nine-time Australian Open champion who was controversially deported on the eve of this year's tournament.

"Because he is one of the greatest champions, as is Roger Federer and Rafa Nadal, and I thought I am going to make him (Auger-Alliassime) work.

"If he wants to win it he needs to fight to the last point, I'm going to make him tired for the next match.

"Fight to the last point and it worked.

"I managed to raise my level during the game, especially in the (third set) tiebreak, and when they closed the roof I felt my momentum change in my game and just started playing better."

It was only Medvedev's third five-set victory in 10 matches going the distance at Grand Slams.

Auger-Aliassime held match point at 5-4, 40-30 in the fourth set, but Medvedev fought it off to make a pressure hold.

Medvedev got a crucial service break in the 11th game when a Auger-Aliassime forehand was wide for the Russian to serve out and force a fifth set on his fourth set point.

Medvedev fought off three break points before getting the crucial break in the next game when Auger-Aliassime double-faulted on break point to lead 2-1 in the final set.

But Auger-Aliassime fought to the bitter end, even holding two break points as Medvedev served out for the match.

It has been a ground-breaking Grand Slam for the rising 21-year-old Canadian.

He beat former US Open champion Marin Cilic for the first time in four encounters in the previous round and looked as if he could repeat the stat against Medvedev, to whom he had also lost on three occasions.

Medvedev will face Tsitsipas in the semi-finals at the Australian Open for the second year in succession after beating him at the same stage in the tournament on the way to the 2021 final where he was beaten by Novak Djokovic.