Matteo Berrettini bowed out of the ATP Finals on a high note by claiming his first victory of the tournament, ending Dominic Thiem's 100 per cent record in the process.

Thiem, who had already qualified for the semi-finals for the first time at the O2 Arena with magnificent victories over Roger Federer and Novak Djokovic, was beaten 7-6 (7-3) 6-3 by an inspired Berrettini on Thursday.

The exertions put into defeating two of the all-time greats appeared to have taken a toll on the fifth seed, Berrettini capitalising to become the first Italian to win a match at the season-ending event.

Tournament debutant Berrettini struck 30 winners - 17 off his powerful forehand - and was broken only once, ending a successful season by levelling their head-to-head record at 2-2.

Federer and Djokovic will battle it out in the second session for the right to join Thiem in advancing from Group Bjorn Borg in London.

Berrettini seized control in the opening set by breaking to love for a 5-4 lead, a cross-court winner, following up one on his backhand side, drawing applause from his opponent.

The eighth seed failed to consolidate, netting a forehand volley after an excellent return from Thiem, but Berrettini put that behind him by bossing the tie-break, wrapping it up with an ace.

Berrettini's blistering forehand continued to fire in the second set and he broke to lead 4-2 following rasping winners off both wings, then ended his fruitful campaign with a drop shot that Thiem was unable to chase down.