World number 114 Aslan Karatsev is into the semi-finals of the Australian Open with a historic 2-6 6-4 6-1 6-2 win over 18th seed Grigor Dimitrov.

The match was a fine duel until the middle of the third set when Dimitrov pulled up with a slight back injury which quickly became a real problem.

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But ultimately his injury restricted his mobility and paved the way for Karatsev, who becomes the lowest ranked player to reach the Australian Open semi-finals since Patrick McEnroe in 1991.

The Russian, who also knocked out Diego Schwartzman and Felix Auger Aliassime en route to the quarters on his Grand Slam debut, will play either Novak Djokovic or Alex Zverev in the semi-finals.

Karatsev becomes the fifth player in history to qualify for a Grand Slam and reach a semi-final.

Highlights: Karatsev's dream run continues with Dimitrov win

Karatsev was making numerous unforced errors in the first set and the Bulgarian 18th seed took complete control.

But at 1-0 down in the second, a 12-minute game when Karatsev saved five Dimitrov break points proved pivotal as the Russian got into a rhythm and started firing off his forehand. He broke the Dimitrov serve twice which proved enough to level the tie.

Dimitrov's back injury then developed. He was faltering on his serve and was left wandering around the Rod Laver Arena court listlessly in the 30 degree Celsius heat.

The contest was essentially over when the 29-year-old Bulgarian, who knocked out Dominic Thiem in straight sets in the fourth round, played on even after the lengthy medical break at the end of the third set.

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KARATSEV: AN UNBELIEVABLE FEELING

"It’s an unbelievable feeling,” Karatsev said post-match.

"It’s the first time playing the men’s draw and the first time the semis.

"It was a really tough one in the beginning for me. I held my nerves. It was still tricky and then in the second set I tried to find a way to play and then the third I felt better. The heat was too much. I just try to play every match.”

'It's an unbelievable feeling' - Karatsev on reaching semi-finals

HENMAN: AN AMAZING STORY

"It’s an amazing story," Tim Henman said in the Eurosport Cube.

"When you think he had to play for qualifying in a different venue in Doha and then he’s just played incredible tennis.

"He talks about nerves and the heat out there and got a bit of luck with Dimitrov getting injured with the back. He’s very calm but he kept going."

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