Aslan Karatsev makes history after beating injured Grigor Dimitrov to reach Australian Open semi-finals

Russian qualifier will face either defending champion Djokovic or US Open finalist Zverev for a place in the final

Aslan Karatsev celebrates victory over Grigor Dimitrov in the Australian Open quarter-finals. AFP

Russian qualifier Aslan Karatsev continued his fairytale run at the Australian Open by becoming the first man to reach a Grand Slam semi-final on debut on Tuesday.

The world No 114 fell a set behind to Grigor Dimitrov but the Bulgarian 18th seed sustained a back injury that put paid to his hopes of reaching the Australian Open last-four for a second time. Karatsev took full advantage to win 2-6, 6-4, 6-1, 6-2 and will face either top seed and defending champion Novak Djokovic or German seventh seed Alexander Zverev.

"Unbelievable feeling, first time in semis. Incredible," said Karatsev. "It was tough at the beginning for me to hold my nerves, but I tried to find a way to play."

In making the last four, he became just the second qualifier to do so at the Australian Open after Bob Giltinan in 1977. He is also the lowest-ranked man to make the semis at a Slam since Goran Ivanisevic at Wimbledon in 2001 when ranked No 125.

A virtual unknown before the tournament started, Karatsev has spent the bulk of his professional career fighting for points on the ATP Challenger Tour.

But he has played the tournament of his life in Melbourne, blitzing eighth seed Diego Schwartzmann and 20th seed Felix Auger-Aliassime on his way to meeting Dimitrov.

Dimitrov served to love to open proceedings but Karatsev fixed his radar and broke for 2-1 when the Bulgarian fluffed a forehand.

But the advantage only lasted until the next game when Dimitrov levelled then broke again for 4-2, winning five games in a row to take the opening set in just 33 minutes.

The Russian was guilty of too many loose shots and had trouble landing his forehands.

But he is a fighter and refused to go quietly, breaking for a 3-2 lead in the second on the back of a wild Dimitrov volley then breaking again to unexpectedly secure the second set.

His persistence began irritating Dimitrov, who started muttering to himself as frustrations crept in and he went 3-1 down in the third set.

The Bulgarian then began struggling as the set wore on and was barely able to serve at 1-5 before taking the medical timeout.

The 29-year-old returned but never looked like getting back in the match.