Aslan Karatsev became the first grand slam debutant in the Open era to reach the semi-finals after beating an injured Grigor Dimitrov at the Australian Open.

Dimitrov won the first set but became increasingly hampered by a back spasm and during the third and fourth sets was struggling to serve and move around the court.

He persevered to the end but there was no doubt about the outcome as Karatsev continued one of the most remarkable grand slam runs with a 2-6 6-4 6-1 6-2 victory.

The 27-year-old Russian has plied his trade in the lower reaches of the sport for his whole career, never breaking into the top 100, only to come through qualifying and storm through the draw at Melbourne Park.

Speaking on court, Karatsev said: “It’s an unbelievable feeling. It was really tough at the beginning for me to hold the nerves. I tried to find a way to play in the second set and then in the third set I saw he felt the back.”

At 114 in the world, Karatsev is the lowest-ranked man to reach the semi-finals at a slam since Goran Ivanisevic won Wimbledon in 2001 while he is only the second qualifier to make the semi-finals in Melbourne after Bob Giltinan in 1977.

His scalps have included Diego Schwartzman, Felix Auger-Aliassime and now Dimitrov and, with both his potential semi-final opponents Novak Djokovic and Alexander Zverev also dealing with injuries, it is not impossible he could go further.

“I try not to think about (that),” he said with a smile. “I try to play every match, going from match to match.”

Dimitrov was left to rue another missed opportunity at a slam having reached the last eight without dropping a set.

He said of his back spasm: “It started yesterday out of the blue. It was just a regular movement. Just super unlucky.

“I felt great over all the past days. I felt I was on a good path. We’ve done great work. I couldn’t put my socks on before the match, so I knew it was going to be a tough moment for me. I tried, but it was not good enough.

There were few signs of any problems during the first set but the momentum shifted during the second and Dimitrov became increasingly affected. He took a medical time-out at the end of the third set but there was little that could be done.

Asked why he did not retire, the Bulgarian said: “I don’t like quitting. I’m definitely causing more harm on myself and I think on my team, but you get stubborn. You’re a competitor.

“When you’re on the court sometimes you don’t think straight and, in that particular moment today, I just didn’t want to give up. I couldn’t give up.”

Dimitrov was keen to stress the focus should be on Karatsev, saying: “That was his day today. Yes, I struggled – that’s fine. I’m admitting it, I’m taking it in. But please, give the credit for him today.”