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.
PSG retain Champions League title with shoot-out win over Arsenal
Paris St Germain held their nerve in a cagey Champions League final to retain the title by beating Arsenal 4-3 on penalties as Saturday’s showdown ended 1-1 after extra time, cementing the French side's status among Europe's modern greats.
French Open champion Gauff knocked out by Potapova in third round
Defending French Open champion Coco Gauff has been knocked out of the Grand Slam following a 4-6 7-6(1) 6-4 loss to Anastasia Potapova in the third round at Roland Garros on Saturday.
Sabalenka sees off Kasatkina to reach French Open fourth round
Aryna Sabalenka has cut through the French Open chaos as the world number one beat Australia's Daria Kasatkina 6-0 7-5 on Saturday to seal her place in the fourth round after seismic upsets in the previous two days at Roland Garros.
Parry stuns Anisimova to reach first Grand Slam fourth round at French Open
Diane Parry, the last Frenchwoman standing in the French Open women's draw, has pulled off a stunning 6-3 4-6 7-6(3) victory over American Amanda Anisimova on Saturday, advancing to the fourth round of a Grand Slam for the first time in her career.
Osaka survives three-set scare against teenager Jovic
Naomi Osaka has dazzled with an all-gold outfit but had to dig deep for a hard-fought 7-6(5) 6-7(3) 6-4 victory over American teenager Iva Jovic on Saturday to reach her first-ever French Open fourth round.
