Rafael Nadal lost to Felix Auger-Aliassime for the first time as his poor run of results continued at the ATP Finals in Turin, where he looks set for a group-stage exit.
In the Green Group, Auger-Aliassime ran out a 6-3 6-4 winner over the 22-time grand slam champion, whose uncle Toni Nadal is on his opponent's coaching team.
Nadal came to Italy with a chance to snatch the year-end number one ranking from Carlos Alcaraz but needed to win this tournament, and defeats to Taylor Fritz and now Auger-Aliassime have almost quashed that prospect.
On Tuesday, the 36-year-old suffered a fourth successive singles defeat, which began with a US Open last-16 exit to Frances Tiafoe and was followed at the Paris Masters by a loss to Tommy Paul.
Auger-Aliassime was beaten in his opening match by Casper Ruud, but he came from 40-0 behind to break for a 5-3 lead in the opener of this contest, before serving out for the set comfortably enough. A break early in the second set put him on course to wrap up the match, with Nadal struggling to make an impact.
This was just a third meeting between Nadal and Auger-Aliassime on the ATP Tour, with Nadal winning both previous contests, including an epic five-set contest in the French Open fourth round in May.
The result this time, however, means Nadal has lost consecutive matches in the round-robin stage of the ATP Finals for the first time since 2011. With a 0-2 record, his only remaining hope of progress hinged on Ruud losing to Fritz later on Tuesday, which would offer Nadal a slim hope going into his final Green Group match against Ruud.
Auger-Aliassime - 15/2
Nadal - 1/4
Auger-Aliassime - 32/2
Nadal - 13/4
BREAK POINTS WON
Auger-Aliassime - 2/4
Nadal - 0/5