Defending champion Novak Djokovic showed yet more mental and physical resilience to beat German sixth seed Alexander Zverev and reach the Australian Open semi-finals.
The top seed fought back to win 6-7 (6-8) 6-2 6-4 7-6 (8-6) in Melbourne.
The Serb will face Russian qualifier Aslan Karatsev, who beat an injured Grigor Dimitrov, on Thursday.
Karatsev, ranked 114th in the world, is the first man in the Open era to reach the last four on his Grand Slam debut.
Few will fancy Karatsev – who largely plies his trade on the second-tier ATP Challenger Tour – to continue his dream run by beating eight-time champion Djokovic.
The 33-year-old world number one looked far from comfortable against Zverev, largely down to the German’s big serving and probing groundstrokes, rather than the abdominal injury which has bothered him throughout the tournament.
But a defeat by Karatsev on Rod Laver Arena – a court which Djokovic says “feels like home” after his domination of the tournament over the past 13 years – would be a seismic shock ranked among the game’s great upsets.
Reaching the last four is a remarkable achievement for Karatsev, who grew up playing tennis in Israel after moving there as a three-year-old.
After moving back to Russia with his father aged 12, he trained in Rostov and Moscow as a teenager before continuing a nomadic career which has seen him work with coaches in Spain, Germany and Belarus.
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 last four since Patrick McEnroe, then ranked 114th, did so in 1991.
“It’s amazing that I reached the semi-final from qualifying. I’m just trying to enjoy the moment and not thinking about that too much and playing from round to round,” said the 27-year-old.
“Four months ago I was ranked 116th and my first step was to go to the top 100 by the end of the year 2020. But it didn’t happen.”
Karatsev’s progression was helped by the injury problems for an upset Dimitrov, who was struggling to move by the end of the match after receiving treatment on his back.
Karatsev himself looked fatigued in a poor first set, with Dimitrov reeling off five games in a row to take the opener.
Karatsev 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, repeatedly mouthed “I’m sorry” at his coaching box and struggled to walk up the stairs at the end of the match.
“I got a back spasm yesterday at some point and that was it. We couldn’t fix it on time,” said Dimitrov.
“It happened early in the match. It kept on progressing, and it was unstoppable.”