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.
An upset Dimitrov was struggling to move by the end of the match after receiving treatment on his back.
The 27-year-old 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.