World number one Novak Djokovic of Serbia was beaten for only the fourth time this year as Russian Daniil Medvedev pummelling him to a shock 6-3 6-3 defeat at the ATP Finals.
The Serb hit 24 unforced errors and five double faults loss to fourth seed Medvedev in London. Shortly after news broke that Djokovic had been nominated for a return to the ATP the player council he had quit in August, he took to the court at the O2 Arena hoping to seal his passage into the semi-finals of the prestigious year-ender.
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.
The permutations at this event are often mind-bendingly complicated but this year it is straightforward.
With the two group winners already decided after Dominic Thiem clinched Group London 2020 with victory over Nadal on Tuesday, there are two winner-takes-all matches to determine the remaining semi-finalists.
Before Djokovic and Zverev meet on Friday, 20-time Grand Slam champion Nadal and defending champion Stefanos Tsitsipas face each other on Thursday.
In, the other match Thursday US Open champion Thiem takes on already eliminated Russian Andrey Rublev.