Daniil Medvedev started the match well, but a moment of slackening and some disappointment cost him the 1st set. Thiem punished a few mistakes by the Russian by forcing a break and was lucky on set point, when he had the net tire on his side.
With the set win in his pocket, Thiem was in control. Yet the Austrian failed to count Medvedev out. At 3-3 in set 2, he was unable to cash in on two break chances and the Russian then dragged a decisive 3rd set out of the fire in the tiebreaker.
In that 3rd set Thiem struggled a lot at a few breakpoints from Medvedev, but at the 6th chance it was hit anyway. Thiem was unable to rectify the break and thus lost the final of the Masters for the two years in a row.
Medvedev, who has not yet been able to win a grand slam tournament in his career, is the deserved laureate of the ATP Finals. On the way to his overall victory, he beat the top 3 of the ATP ranking with Djokovic, Nadal and Thiem. The 24-year-old Russian himself is number 4 in the world.