Dominic Thiem recorded a 6-3 1-6 6-4 win Gael Monfils at the Barclays ATP World Tour Finals to boost his chances of reaching the semi-finals.

The 23-year-old Austrian recovered from a second-set wobble to see off his Monfils, who like Thiem is appearing at his first World Tour Finals.

Despite having lost both his matches, Monfils is not yet eliminated but will have to beat Novak Djokovic on Thursday and hope other results go his way.

The unpredictable Frenchman, who appeared to be struggling physically at times, played a major part in his own downfall by serving three double faults in the final game and then driving a backhand long.

Thiem said: "I think it was a very close match. I had a much better start, he played a good second set. The third was very tight, luckily he helped me a little bit in the last game."

The eighth seed will take on fourth seed Milos Raonic on Thursday in what could be a straight fight for a place in the last four.

Thiem was rewarded for greater consistency with a break for 4-2 in the first set and it was clear all was not well with Monfils when he hobbled through the final game.

The Frenchman came into the tournament nursing a rib injury and admitted after his opening loss to Milos Raonic that he was not fully fit.

The O2 Arena has played host to many weary bodies since the tournament moved to London in 2009.

But Monfils roused himself and, helped significantly by his opponent, raced into a 4-0 lead in the second set.

Thiem had a similar lapse in his opening match against Djokovic, winning a very tight opener and then losing the second set to love.

The Austrian blamed a drop in energy - no surprise given a hectic schedule which has left him running on empty in recent weeks.

Monfils wrapped up the set with three successive aces to keep alive his hopes of reaching the semi-finals, and he was beginning to pull off a few show-stopping shots.

The deciding set was a much better contest, and Monfils withstood three break points in the eighth game to hold for 4-4. But serving to stay in the match two games later he came unstuck.