Rafael Nadal began his quest to fill the one blank on his glittering CV in impressive fashion with a crushing defeat of tournament debutant Andrey Rublev at the ATP Finals.
Spanish 20-time grand slam champion Nadal was in menacing form as he dispatched 23-year-old Rublev 6-3 6-4.
Nadal has qualified for the season-ending event for a record 16 years in a row, although he has missed it six times through injury, but has yet to lift the trophy - he has been a runner-up twice.
Rublev has won more matches and more titles - five - than any other player this season to surge into the top 10, but he was not allowed to settled into the contest.
World No.2 Nadal broke serve in the sixth game of the match on his way to the opening set.
Rublev hurled his racket to the court after being broken for 4-2 and never threatened a recovery.
The Russian dropped serve at the start of the second before a clinical Nadal wrapped up victory in his opening round-robin match in 77 minutes.
Earlier on Sunday, US Open champion Dominic Thiem defeated last year's ATP Finals champion Stefanos Tsitsipas in three sets.
Thiem outlasted Tsitsipas 7-6 (7-5) 4-6 6-3 in a rematch of last year's decider.
This is the 12th and last year that the ATP Finals is played at the 02 Arena before moving to Turin, Italy, next year.
Because of the coronavirus pandemic there are no fans inside the 20,000-capacity venue this time - meaning the normally raucous atmosphere has been replaced by an eerie silence interrupted only by muted applause from the players' boxes between points.
"It's the easiest year for a long time, today was my 30th match on Tour which is not a large number," Thiem told reporters after his win over Tsitsipas.
"But mentally it's tough because you get so much energy from the fans in the stadium if you have a huge win like today, so much positive energy and all of this is missing."
There are also no line judges, as the tournament is using electronic line calling for the first time.
"The electric line call, I like it a lot," Thiem said.
"Because, well, there are no wrong decisions anymore. I mean, if the electric system calls it out, it's out."