World No. 1 and home favorite Jannik Sinner began his bid to win the Association of Tennis Professionals (ATP) Finals for the first time with a 6-3, 6-4 defeat of tournament debutant Alex de Minaur on Sunday.

Sinner, runner-up to Novak Djokovic in the prestigious year-ending tournament last year, dropped behind early in the first set but quickly hit back to dominate the contest.

The Italian, who won this year's Australian and US Open titles to open his Grand Slam account, completed victory with an ace to make it eight wins out of eight against De Minaur.

Sinner, 23, had not played a competitive match for four weeks since taking the title in Shanghai, his seventh of the season, and there was some early rust as he dropped serve to trail 2-1 in the opening set.

Nonetheless, he broke back immediately and his power from the baseline proved too much for De Minaur thereafter as he was roared on by the crowd in the 13,000-seater Inalpi Arena.

"Considering I hadn't played for four weeks, I'm very happy," Sinner said at court side. "I started off with some unforced errors at the beginning of the match but I stayed there mentally knowing that at some point my tennis would arrive. It arrived quite early and started to return very well. Today I'm pleased with the win and it will give me confidence."

Sinner is hoping to cap a superb year on the court, although a cloud still hangs over the Italian who was cleared of wrongdoing by an independent tribunal after testing positive for the anabolic agent clostebol in March this year.

The tribunal, organized by the International Tennis Integrity Agency (ITIA), accepted Sinner's explanation that the banned substance entered his system from a member of his support team through massages and sports therapy.

The World Anti-Doping Agency (WADA) has since appealed the 'no fault or negligence' decision to the Court of Arbitration for Sport (CAS).

Taylor Fritz off to winning start after Daniil Medvedev's meltdown

American Taylor Fritz won his first match in the group stage when he beat Daniil Medvedev 6-4, 6-3 after the Russian lost his cool and risked getting defaulted because of his bizarre antics.

Medvedev, who was the ATP Finals champion in 2020 and runner-up the following year, lost his composure after a string of double faults in the first set as Fritz beat the Russian for the first time in his career.

The victory was the 50th for US Open finalist Fritz in 2024 and his eighth top-10 win of the season.

"I definitely felt like at 5-3 (in the second set) he was going to reset and try as hard as he could to break me and I just had to kind of tell myself, 'He's not going to just be done with the match'," Fritz said. "It's very easy sometimes when someone's doing that to kind of relax and think that they're just going to be done and then you drop your level. I just had to try to tell myself to stay focused at 5-3 and play a really good game because he was going to fight for that game. Luckily, I served a great game."

The opening set went without a single break point until the final game, with Fritz especially dominant on his first serve while Medvedev struggled with his second serve. However, with Fritz leading 5-4, Medvedev won a long rally with a beautiful drop shot before he imploded and served three double faults to hand the set to his American opponent.

Medvedev was so incensed that he smashed his racket on the ground as he finished the set with seven double faults. The Russian soon lost his composure again in the second set and began to unravel, breaking a microphone with his racket and being given a point penalty.

Medvedev kept pushing his luck and tested the chair umpire's patience by continually throwing his racket up in the air and dropping it. He also faced a Fritz serve holding the racket by its head as the Turin crowd began to whistle and jeer.

"I get angry, frustrated. This time completely with myself, not with anyone. Just with myself," Medvedev told reporters. "I was like, 'Whatever, I lost the match. I don't care'. I mean, you have to finish the match. You cannot withdraw, no? I just finished the match."

Fritz eventually put Medvedev out of his misery when he served to love in the final game.