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 in a match which is live on BBC Two.
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.
BDST: 1220 HRS, NOV 16, 2019