Stefanos Tsitsipas wins ATP Finals title: Greek defeats Dominic Thiem in three sets at The O2

Stefanos Tsitsipas has won the ATP Finals after beating Dominic Thiem in a thrilling final at The O2 Arena.

The 21-year-old suffered an early setback after losing the first-set tie-break. But the Greek youngster channelled his frustration into his game, bouncing back to win the second in just 29 minutes and force a deciding set.

His phenomenal serving showed he would be difficult to beat and when the match went to a final set-tiebreak, he held his nerve to seal a 6-7, 2-6, 7-6 success in two hours and 35 minutes to win the title on his debut.

By doing so, he becomes the first player from his nation to win the tournament and the youngest champion since Lleyton Hewitt in 2001.

After a full week of packed crowds and dramatic action, The O2 arena wasn't close to being at capacity and the lack of a top-three player in the showpiece fixture was probably to blame. But these were two players who could soon be Grand Slam winners and it promised to be an intriguing battle.

Neither player had won a title that held the same significance as this, although Thiem - twice a Grand Slam finalist - was no stranger to the pressure. The pair are close off and on the court, but both players pledged to put their friendship to one side as they prepared to go at it hammer and tongs.

Tsitsipas showed just how strong he was going into the semi-finals by winning his first two matches and, having already qualified, took Rafael Nadal all the way in a three-hour marathon.

But Thiem's confidence would have been sky high, having overcome Federer, Djokovic and last year's champion Alexander Zverev on his route to the final.

Thiem looked a little nervous, making errors from the net that only come from a mental block and found himself a break point down. But the Austrian fought back to deny Tsitsipas an early advantage.

Tsitsipas was the master of saving break points and he had to put his abilities to the test when Thiem earned two at 3-3. Sure enough, he lived up to the billing, fighting with a mixture of grit and class to stay on serve.

In the next game, it was Thiem's turn to prove his resilience. Tsitsipas had the double-breakpoint opportunity this time, but some outstanding work - with a volley at full-stretch - at the net saved his skin.With nothing in it, there was no real surprise when the players took it to a tie-break. Even then, sudden death was needed at 6-6. But when Tsitsipas made a colossal blunder on the backhand, Thiem took full advantage and wrapped up the first set after 63 minutes.

For the first time, Tsitsipas looked frustrated. But crucially, he managed to channel it into his game and began his fightback immediately, taking a double break inside the first 13 minutes on his way to a 4-0 lead in the second set.

Tsitsipas was looking utterly dominant and didn't drop a point on his serve until the final game, and only two in the entire set, as he forced a deciding set.

The 21-year-old certainly had the momentum but there was a feeling Thiem was holding back, conserving his energy for the final set after conceding the early double break.

He had to keep his nerve to avoid a similar occurrence in the second set as a determined Tsitsipas earned two early break points. But Thiem was adamant he wouldn't let it slip this time, recovering by using the power of his serve to squeeze errors out of Tsitsipas.

Thiem showed an admirable sense of courage to snatch back the break and take three games in a row as the momentum swung in his favour.

But Tsitsipas rediscovered his composure, taking the lead in some exceptional rallies on display and brought it back to 4-4. Thiem served impeccably to lead 5-4, though, to throw the pressure right back onto the young Athenian's shoulders.

There was very few signs of him losing his nerve and it was perhaps fitting that an extremely tight contest went to a final-set tiebreak.

Thiem fought back from 4-1 down to level the tiebreak but made two crucial errors on the forehand and he knew the game was up. Tsitsipas had two serves left and making them both would see him triumph. An error from Thiem. Two match points. First serve? Out. Second serve? In. Thiem, with a rush of blood, strikes long and the Greek collapses to the floor. The crowd had got their champion after a marathon match in London and his name was Stefanos.

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