Novak Djokovic has made the ideal start in his quest to win a record-equalling sixth ATP Finals title.
The world number two easily beat Italy's Matteo Berrettini in straight sets at the O2 Arena in London.
However, things weren't as rosy for Roger Federer, who was beaten by Dominic Thiem in his tournament opener.
It's the second year in a row that the seven-time Dubai Duty Free Tennis Championships winner has lost his opening match at the ATP Finals.
Swiatek, Gauff through to Australian Open 2nd Round
World number two Iga Swiatek advanced to the second round of the Australian Open on Monday with an unconvincing 6-3 6-4 win against first-time opponent Katerina Siniakova on John Cain Arena.
Sinner survives tough test, Alcaraz eases through
Jannik Sinner launched his Australian Open title defence with a 7-6 7-6 6-1 win over Nicolas Jarry on Monday in a match that put the players' contrasting doping cases in the spotlight, while Carlos Alcaraz began his bid to complete a career Grand Slam with a 6-1 7-5 6-1 win over Kazakh Alexander Shevchenko.
DP World ILT20 Season 3 kicks off
The stage was set on Sunday for the highly anticipated return of the DP World ILT20 Season 3, promising to mesmerise cricket fans across the globe.
Amorim sees progress in Man United's shootout win at Arsenal
Manchester United boss Ruben Amorim said his team are still improving, as Sunday's dramatic FA Cup penalty shootout victory over Arsenal points to a more positive future after a difficult start to life at Old Trafford.
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