An error-prone Novak Djokovic was beaten for only the fourth time this year as Daniil Medvedev reached the semi-finals at the ATP Finals.
The Serb hit 24 unforced errors and five double faults in a 6-3 6-3 loss to fourth seed Medvedev in London.
World number one Djokovic, 33, can still qualify for the last four if he wins his final round-robin match against Alexander Zverev on Friday.
Zverev earlier boosted his own hopes with victory over Diego Schwartzman.
The German fifth seed overcame a poor second set to claim a 6-3 4-6 6-3 win against the Argentine, who is now unable to reach the knockout stage after Medvedev’s win at the O2 Arena.
Watch the highlights of the game:
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