LONDON -- Nearing defeat, Daniil Medvedev suddenly switched tactics at the ATP Finals and collected the biggest title of his career by beating U.S. Open champion Dominic Thiem 4-6, 7-6 (2), 6-4 on Sunday. The fourth-ranked Medvedev became the first player to beat each of the men who were Nos. 1-3 in the season-ending championship -- and only the fourth to do it at any tour event in the past 30 years.

The comeback against No. 3 Thiem, which lasted more than 2½ hours, added to victories Medvedev produced against No. 1 Novak Djokovic in the round-robin portion of the tournament and No. 2 Rafael Nadal in Saturday's semifinals on an indoor hard court without spectators, who were barred because of the coronavirus pandemic.

Medvedev, 24, went 5-0 in all, quite a turnaround from a year ago, when he went 0-3 at the ATP Finals. The tournament now ends its 12-year run in London, moving to Turin, Italy, next year.

Medvedev, of Russia, closed 2020 by going 10-0 in November, including seven wins against members of the Top 10. He had zero victories over Top 10 opponents over the preceding 12 months.

Thiem's defense and power from the baseline put him on top early, and strong serving at key moments allowed him to save the first eight break points he faced. But Medvedev, the runner-up to Nadal at the 2019 US Open, finally converted on his sixth break chance of the third set -- and ninth of the match -- by sneaking forward behind a return, making a forehand volley winner and going up 3-2.

That was enough, because Medvedev never faced a break point the rest of the way; he finished with 12 aces.

A key shift came in the second-set tiebreaker, thanks to a change in style from Medvedev.

Thiem had grabbed a 2-0 lead there, before Medvedev stormed back, using an element of surprise by rushing to the net more often than usual -- both behind serves and returns -- and reeling off the next seven points. Medvedev continued with that strategy to great effect in the final set, too.

It seemed to throw off Thiem, who had won three of the pair's previous four matches, including in straight sets in the semifinals in New York in September en route to his first Grand Slam trophy. In the second set Sunday, Thiem had break opportunities to take a 4-3 edge, but he badly missed a short shot on one, reacting by putting his hands on his hips, and Medvedev produced an ace on the other. Thiem stumbled and tumbled to the court in the next game, but appeared to be OK.