Roger Federer got the better of Novak Djokovic 6-4, 6-3 in Thursday's heavyweight clash at the ATP Tour Finals, with the former advancing into the last four at the expense of the latter. 

The 20-time Grand Slam champion was comfortably the better player on the night, as he served impeccably and capitalised on a below-par performance from his rival. It means Federer has a chance to win a seventh ATP Tour Finals title, with Djokovic's year ending in early elimination and disappointment.

Earlier in the day, Matteo Berrettini finished his tournament with an impressive 7-6 (3), 6-3 success over Dominic Thiem. Thiem had already secured his spot in the last four with stunning wins over both Federer and Djokovic.

Here are the results from a memorable day at the O2 Arena in London, some highlights of the play and the schedule for Friday's fixtures.

ATP Tour Finals 

Thursday Results

(3) Roger Federer bt. (2) Novak Djokovic: 6-4, 6-3

(8) Matteo Berrettini bt. (5) Dominic Thiem: 7-6 (3), 6-3

Friday Schedule

(1) Rafael Nadal vs. (6) Stefanos Tsitsipas 

(4) Daniil Medvedev vs. (7) Alexander Zverev 

Thursday Recap

The early stages of these high-profile contests are often so key, especially in three-set showdowns. Federer was the man who settled the quickest.

Djokovic's two double faults allowed Federer to break and then consolidate, moving 3-1 ahead. From there, he settled into a sensational rhythm on serve and prevented Djokovic from using his exceptional returning skill.

Indeed, the Swiss veteran kept on chipping away on serve and eventually coasted to the set, winning it 6-4. Former player Greg Rusedski provided the numbers behind an almost flawless stanza of accuracy with the ball in hand from Federer:

The Swiss didn't relent in the second set either, as he was quick to seize on some more hesitancy in the Djokovic game.

With a one-set lead intact, Federer was also starting to be more aggressive in his play and constructed this point, which was the foundation for another break of serve in the next game:

Tennis journalist Christoper Clarey commented on the freedom with which the great man was playing in such high-pressure circumstances:

At this stage, Djokovic was noticeably demoralised, as even someone as strong as him in return play was unable able to make dent in the 38-year-old's serve. The physical effects of Tuesday's epic clash with Thiem appeared to be taking their toll, too.

Federer, knowing how dangerous Djokovic can be, didn't let up and, to hammer home his dominance on the night, he put the match to bed with another break of serve.

Ben Rothenberg of the New York Times noted the win over Djokovic has been a long time coming for Federer and the Swiss' win was good news for Rafael Nadal:

Earlier in the day, Berrettini put an end to Thiem's impressive winning run and in doing so made some history at the ATP Finals, per Tennis TV:

There was nothing between the players in the first set and both felt the nerves late on in it, as they each earned breaks of serve. In the tiebreak, Berrettini recovered after previously failing to serve out the match, moving to a 6-1 lead; at the third time of asking, he snatched a set point.

Perhaps with the semi-finals in mind, there wasn't a huge amount of resistance from Thiem in the second stanza. However, Berrettini was a worthy winner and will be delighted to have capped off his memorable year with a victory.