How it happened: Tsitsipas edges Thiem in three sets to win ATP Finals

Stefanos Tsitsipas has won the ATP Finals, defeating Dominic Thiem in just the third final-round final-set tiebreaker in tournament history, 6-7 (2), 6-2, 7-6 (4).

The champion's speech:

The runner-up's remarks:

8:50 PM: The first mini-break went to Tsitsipas, on a Thiem backhand wide. Another Thiem backhand error gives Tsitsipas a 4-1 lead.

But two points later, Thiem is back on serve, with some bold and deep hitting.

At 4-4, Tsitsipas returns back at the body, and the Thiem forehand reply is long. Another Thiem forehand error gives Tsitsipas two match points.

And in his first-ever appearance at the ATP Finals, after a Thiem return error, Stefanos Tsitsipas wins, 6-7 (6), 6-2, 7-6 (4).

8:40 PM: The last time the season-ending championships were decided in a tiebreak, David Nalbandian beat Roger Federer in 2005. This is only the third time a tiebreaker has ever been needed in a final.

Here we are.

8:36 PM: Stefanos Tsitsipas, your move. Since 3-3, it's been an exchange of hot potato between the players, and Dominic Thiem threw it back, with an ace.

8:32 PM: Drama-free hold from Tsitsipas, for 5-5. Tiebreaker is played at 6-6, in case you're wondering. And given all the different ways final sets are decided at majors, I can understand if you're wondering.

8:30 PM: Thiem holds, leads 5-4. Who blinks first?

8:26 PM: Tsitsipas holds for 4-4.

8:21 PM: Huge push from Thiem. Third straight game from 1-3 down, and very quickly, the pressure is back on Tsitsipas. Have a look at that tweet from Chris Oddo, on deciding sets, during this changeover.

8:19 PM: Tsitsipas hitting shorter in the court—with something to lose, he seemed to be feeling the moment—and Thiem recognizes the opportunity. Thiem, feeling free of pressure, hits big and snags the break. It's now 3-3.

8:12 PM: A bit of a stabilizing sequence from Thiem, who holds after Tsitsipas consolidates. Tsitsipas to serve up 3-2.

8:05 PM: We're back in the first set, it seems, as Thiem's serve is under constant duress. Falls behind 0-30, and 15-40.

With big hitting from baseline, an eventual move forward, and a putaway volley, Thiem saves the first break chance.

With a low-percentage backhand that finds the net on his first shot after a second serve, Thiem can't save the second.

All the momentum with Tsitsipas, who will serve at 2-1.

8:00 PM: Tsitsipas answers with a far simpler hold. 1-1.

7:58 PM: Thiem with a break-point saving, and ultimately successful hold. 1-0. Emblematic of this third set? I could see that.

7:46 PM: We're heading to a third set. Check out these stats:

7:42 PM: Thiem gets on the board with a pair of holds, but Tsitsipas to serve for the second set, one in complete contrast to the opener.

7:34 PM:

7:30 PM: Tsitsipas is simply feeling it right now. Breaks Thiem for a 3-0 lead with a series of uber-confident shots, including a mid-court lob that results in a putaway volley. The Greek isn't thinking, he's just swinging—which is what every tennis player wants to do.

7:28 PM: Extremely sloppy game from Thiem to begin the second set, and Tsitsipas earns the day's first break, at 15. He holds just as quickly for a 2-0 lead.

7:21 PM, Thiem wins first set, 7-6 (6): Thiem isn't the crispest volleyer in the game, but his game is most effective when he comes forward. His hard, spin-heavy shots are nearly impossible to defend from inside the court, and even the threat of a foray can leave his opponent questioning their strategy. This tactic, in part, leads to a 3-0 led in the tiebreak.

At 5-2, with Tsitsipas serving, Thiem tries a jumping one-handed backhand, which finds the net. It's not until an ace, at 5-5, that Thiem gets back on the board.

And it's with an unreturned serve that Thiem wins the set, on his second set point. That point was the only difference in total points between the two players.

7:10 PM: Thiem falls behind 0-30, and responds with three giant forehands to win the next three points. He goes on to hold—the 12th of the set, overall—and a tiebreak is needed.

7:03 PM: Two more holds; 6-5, Tsitsipas, on serve. While both men have had instances of inconsistency, this has been a very clean first set overall.

6:55 PM: The players remain on serve, and stingy with their backs against the wall. Thiem to serve at 4-5.

6:45 PM: Thiem gets his claws into a Tsitsipas service game for the first time, at 0-30. A poor Tsitsipas forehand down the line floats wide, giving Thiem his first break point of the match. Tsitsipas saves it with a volley winner. He holds, continuing a trend over the past few games, for 4-3.

6:37 PM: After Tsitsipas hold, another Thiem deficit on serve. This time it's a forehand error that puts him down 15-30. It's also another Thiem recovery—he sticks a volley to get game point, and converts the next point for 3-3.

6:28 PM: After Tsitsipas holds, Thiem misses a routine volley to fall behind 0-30. Tsitsipas earns the first break point of the match at 30-40, but Thiem saves it with a heavy forehand on a second-serve point. Thiem goes on to hold for 2-2.

6:19 PM: Two fast holds to begin the final. For as skilled as these two are from the baseline, neither is a slouch on serve, especially on a court that plays quickly.

6:02 PM, London time: Remember when Stefanos Tsitsipas beat Roger Federer at the Australian Open in January? Or when Thiem beat Federer to win Indian Wells in March? I'm not trying to pile on Federer—he's already had a difficult weekend—but those two matches seem like eons ago in the nearly 11-month season that is the ATP Tour.

But those results, and the confidence that came from them, played a part in Tsitsipas' and Thiem's presence at this week's season-ending championships in London. It's been a long year, but these two have saved some of their best tennis for last. That includes their last meeting, in the final of the China Open. Thiem won that match, 3-6, 6-4, 6-1, and leads the head-to-head 4-2. But the competitiveness these two one-handers have shown against each other throughout their short careers, and the fight they've displayed throughout this week against the game's best, should bode well for the potential of today's title match.

Stay tuned to this page for first-ball-to-last coverage.