Team Europe's Matteo Berrettini defeated Team World's Felix Auger-Aliassime in the Laver Cup on Saturday as the tennis world dealt with the hangover from Roger Federer's emotional farewell party.

Federer said a tearful goodbye to tennis late on Friday night when the 20-time Grand Slam champion and doubles partner Rafael Nadal were beaten by Jack Sock and Frances Tiafoe at London's O2 Arena.

The 41-year-old announced earlier this month that he would retire after the Laver Cup due to the knee problems that had kept him on the sidelines since Wimbledon in 2021.

Federer's fitness issues meant he could only play one doubles match, so Berrettini was called into the Team Europe squad to replace the Swiss legend after the last game of his incredible career.

With Federer watching from courtside, Berrettini proved a capable deputy as he defeated Auger-Aliassime 7-6 (13/11), 4-6, 10/7 to give Team Europe a 4-2 lead in the three-day tournament.

The 26-year-old Italian, who finished as the 2021 Wimbledon runner-up, had to dig deep to hold off a spirited challenge from Auger-Aliassime, a 22-year-old Canadian rising star.

Auger-Aliassime, ranked 13th in the world, is one of a group of prodigies hoping to take over from Federer and Nadal as the sport's next generation.

Nadal had opted to pull out of the rest of the tournament after the Federer doubles match for what organisers said were "personal reasons".

The Spanish world number three, who has been struggling with an abdominal injury while his wife is heavily pregnant, was replaced by Cameron Norrie on the Team Europe roster.

- Emotional finale -

On the first day of his life after tennis, Federer could have been forgiven for following Nadal's example and heading off for a well-earned rest.

But Federer showed his passion for tennis is unlikely to fade anytime soon as he sat courtside to support Berrettini with the rest of the Team Europe squad despite the post-midnight finish to his emotional finale.

Federer, who was involved in setting up the Ryder Cup-style Laver tournament, had said "we can all party together" as the 17,500-crowd raised the roof with their acclaim for one of the sport's all-time greats after his final match.

But there was an inevitable hangover at the O2 Arena as the atmosphere during Berrettini's clash with Auger-Aliassime struggled to live up to the great man's swansong.

Federer looked relaxed as he mimicked Berrettini's clenched-fist celebration as the Italian took the first set after Auger-Aliassime saved five set points in the tie-break.

Auger-Aliassime was unfazed by losing that 75-minute opening set and levelled the match in the second set before Berrettini finally closed out the victory in the first to 10 points 'Laver Breaker'.

Later on Saturday at the Laver Cup, Novak Djokovic will return to the court for the first time since winning Wimbledon in July.

Team Europe's Djokovic faces US Open semi-finalist Frances Tiafoe in the singles and then teams up with Berrettini for a doubles match against Sock and Alex de Minaur.

The 35-year-old beat Nick Kyrgios to claim the seventh Wimbledon crown of a remarkable career that includes 21 Grand Slam titles.

But Djokovic, currently ranked seventh, missed the US Open in September due to his unvaccinated status, leaving him to take an enforced two-month break from competitive action.

The former world number one has faced Tiafoe once before in last year's Australian Open second round when the Serb won in four sets.

In the day's other Laver Cup singles match, Norrie, the British world number eight, plays American world number 12 Taylor Fritz.