Alexander Zverev booked his place in the Canadian Open quarter-finals after Francisco Cerundolo was forced to retire early from their last 16 clash.
Cerundolo entered the match with tape on his abdomen and required a medical timeout in the fifth game of the first set, and was unable to recover.
The pair embraced at the net with the match at 5-4, with Cerundolo allowing Zverev to serve out for the opening set before retiring in the first game of the second.
Zverev's victory saw him improve to 38-14 for the year as he edges closer to a second Canadian Open title, having won the event back in 2017.
Up next for the top seed is a mouth-watering clash against defending champion Alexei Popyrin, who upset Holger Rune in straight sets to reach the last eight.
Popyrin, who defeated Andrey Rublev in last year's showpiece match, came from behind to earn a 4-6 6-2 6-3 victory in two hours and three minutes.
The Australian failed to convert any of his break point opportunities in the first set, but recovered well to set up a date with Zverev for a place in the semi-finals.
"I started this week not high on confidence, needing to get a grasp of the mental side," Popyrin said of defending his title. "But this week I kind of just let go of all the pressure.
"After the first set I was p***** [about not breaking]. But when I came back out to return again, it felt like I was in control of the match.
"I told myself to be aggressive on the next break point that I got, and from then on I felt quite comfortable."
Data Debrief: Zverev continues hard-court success as Popyrin wins again
In what looks set to be an intriguing quarter-final matchup, Zverev and Popyrin continued their impressive form in Toronto with their respective last 16 victories.
Zverev has now reached his 20th ATP Masters 1000 quarter-final on hard court, equalling Milos Raonic for the most on the surface of any player born since 1990.
Popyrin, meanwhile, is the first player in the Open Era to win his first nine men's singles main draw matches at the Canadian Open.
He is also the fourth Australian in the Open Era to reach consecutive men's singles quarter-finals at the tournament, after Paul Kronk (1979-80), Mark Philippoussis (1996-97) and Pat Rafter (1998-2001).
