Russian youngster Andrey Rublev signed off from his maiden ATP Finals in impressive fashion by beating Dominic Thiem 6-2 7-5.

The aggressive 23-year-old took full advantage of a rather flat performance by Thiem, who had already sealed his place in the semi-finals with two wins in the London Group.

Defeats by Rafael Nadal and Stefanos Tsitsipas meant Rublev was playing only for pride on Thursday, although the $US153,000 ($A210,484) bonus for a group stage win provided a sizeable incentive.

The world No.8, who won a tour-leading five ATP titles this year, put the hammer down from the start, taking a 4-0 lead on his way to winning the opening set.

Rublev grabbed an early break in the second set but faltered at 4-3 when a netted forehand allowed Thiem to level.

But Rublev broke the Austrian world No.3 again at 5-5 with a thumping forehand, and finished the job a game later.

He will look back on a missed opportunity, having double-faulted when he held a match point against defending champion Tsitsipas in his second match.

Thiem will shrug off the defeat and now has a day off to prepare for Saturday’s semi-final when he will face either world No.1 Novak Djokovic or Alexander Zverev.

Later on Thursday, Nadal faces Tsitsipas with the winner joining Thiem in the semi-finals.