World number 114 Aslan Karatsev beat an injury-hampered Grigor Dimitrov at the Australian Open to become the first man in the Open era to reach the semi-finals on their Grand Slam debut.
The Russian qualifier fought back to shock the Bulgarian 2-6 6-4 6-1 6-2.
An upset Dimitrov was struggling to move by the end of the match after receiving treatment on his back.
Karatsev, 27, will play either world number one Novak Djokovic or Alexander Zverev for a place in the final.
Karatsev himself looked fatigued in a poor first set, with Dimitrov reeling off five games in a row to take the opener.
He had to stave off five break points in a 13-minute service game in the early stages of the second set before taking advantage when Dimitrov's level dipped.
Dimitrov, a semi-finalist at Melbourne Park in 2017, said he had struggled with pelvic spasms in the build-up to the match and could barely roll in a serve as the match progressed.
He repeatedly mouthed "I'm sorry" at his coaching box and struggled to walk up the stairs at the end of the match.
It is, however, a remarkable achievement for Karatsev, who has been playing Challenger events for much of his career.
He has become the second qualifier to reach the Australian Open semi-finals after Australian Bob Giltinan in December 1977.
Karatsev is also the lowest-ranked man to reach the Australian Open finals since Patrick McEnroe, then ranked 114th, did so in 1991.
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