2019 Nitto ATP Finals
Venue: O2 Arena, London
Dates: Nov 10-17
Rafael Nadal missed out on a place in the ATP Finals last four as defending champion Alexander Zverev claimed the remaining semi-final spot in London.
Nadal, who beat Stefanos Tsitsipas 6-7 (4-7) 6-4 7-5 in the afternoon session, needed Daniil Medvedev to beat Zverev to secure a place in the last four.
However, Zverev came through 6-4 7-6 (7-4) to eliminate Nadal and set up a meeting with Dominic Thiem.
Tsitsipas will face Roger Federer in the other semi-final on Saturday.
Swiss Federer, who is bidding for a seventh title at the tournament, plays Greek Tsitsipas from 14:00 GMT. Germany's Zverev takes on Austrian Thiem from 20:00.
World number one Nadal had knocked Russian fourth seed Medvedev out of the tournament with his hard-fought victory over Tsitsipas.
Ultimately, it was a lifeless performance in his opener against defending champion Zverev on Monday that cost Nadal.
Seventh seed Zverev has had a mixed season but put in a convincing performance against Medvedev to advance to the semi-finals.
The German broke Medvedev in the opening game of the match and capitalised as the Russian's serve faltered in the closing stages.
After staving off a break point, Medvedev held his nerve to force a tie-break, but a double fault allowed Zverev to serve out the match.
Zverev, who did not face a break point all match, fell to his knees after the final point, and said afterwards he could "still improve" on his performance.
