Novak Djokovic overcame a worrying knee injury scare and a huge second-set deficit to reach his fourth Olympic Games semifinal on Thursday.
The Serbian top seed defeated Stefanos Tsitsipas 6-3, 7-6 (7/3) but only after aggravating the right knee injury that required surgery in June.
Djokovic needed on-court treatment after slipping on the baseline of Court Philippe Chatrier.
He fell 0-4 and then 2-5 down in the second set but battled back to save three set points in the ninth game.
The 24-time Grand Slam title winner, still looking for a first Olympic gold medal, then raced through the tie-break to record his 12th win in 14 meetings against the Greek.
He will face Italy's Lorenzo Musetti for a place in the gold medal match.