Dominic Thiem
Thiem had no margin for error but his stroke-play did the talking against Monfils.Getty Images

Dominic Thiem remains in contention to reach the last four of the ATP World Tour Finals after outlasting Gael Monfils in three sets at The O2 Arena. Thiem came through 6-3 1-6 6-4 in 89 minutes to stay in the competition and leave the Frenchman contemplating a round robin exit.

In a contest which ebbed and flowed for long periods, it was Thiem who provided the much-needed consistency at the crucial moments and capitalised on constant errors from his opponent. Monfils played with typical flourish but was unable to keep his cool when it mattered most.

Victory for Thiem means Novak Djokovic will qualify for the semi-finals if he beats Milos Raonic in the evening match on Tuesday [15 November]. The Canadian, who has never defeated the 12-time major champion in their previous seven encounters, can also reach the knock-out stage if he wins in two sets.

"It was a very close match," the 23-year-old Thiem said after his first ever victory at the end of season championships in London. "I had much the better of the first set but he improved in the second set. He helped me a little bit in the last game of the match and perhaps I was the luckier one today. I am very happy when I face [Raonic] on Thursday that there is still something going on. I have a chance to get into the semi-finals. I cannot not wait to come out in front of this amazing crowd."

Humbling defeats on their maiden appearances in the season-ending tour finals meant both Monfils and Thiem's future in the tournament hung by a thread heading into day three. Defeat for either player would all-but consign them to a round robin exit and curtail a campaign in which the pair have impressed greatly.

Thiem won the first set against Djokovic before fading badly in his opening match, but was aiming to go one better after breaking Monfils in game five. The 30-year-old Monfils was happy to exchange at the back of the court and that was to be his undoing as the Austrian's power prevailed.

Taking 14 out of 16 points in the middle of the set allowed Thiem to gain the upper-hand and his superiority was enhanced by an apparent injury to Monfils. The US Open semi-finalist was hobbling around the baseline as Thiem was serving out the opening set – with victory looking like a formality.

Whether Monfils' fitness concerns were a ruse to unsettle his opponent, or genuine, was uncertain, however it inspired a rapid and dramatic turnaround in his fortunes. The Paris-born right-hander went on the offensive immediately and that helped him claim a double break at the start of the second set as the rallies between the two began to lengthen.

Monfils had gone from appearing uninterested to being the frontrunner and though he was initially broken back by a re-energised Thiem, three straight aces squared the match. Monfils remained hindered by an apparent calf injury but nevertheless he was a potent force as Thiem sought an avenue back into the contest.

It was now a straight shootout between Monfils' flamboyance and Thiem's consistency, and it was the latter who held his nerve to stay alive in the competition. Three break point chances came and went in game eight for Thiem, but when faced with a match point as Monfils served to stay in the match three double faults followed by a long backhand saw the world number nine prevail.