LONDON (Reuters) - Russian youngster Andrey Rublev signed off from his maiden ATP Finals in style by beating Dominic Thiem 6-2 7-5 on Thursday.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 Rafa Nadal and Stefanos Tsitsipas meant Rublev could not advance but the $153,000 and 200 ranking points for a group stage proved a sizeable carrot. But for a double fault when he had a match point against Tsitsipas on Tuesday, Rublev could now be looking at a place in the semi-finals. Instead he will leave London full of belief after a superb 2020 in which he won a season-leading five titles. “I was so close in my second match. I had match point and I was serving, so it could have been a completely different story if I won two matches,” Rublev said on court.“I would maybe still have a chance to be in the semi-finals. But it’s part of life.” The world number eight, playing again in a drab-looking olive green tee-shirt, put the hammer down from the start and broke the Thiem serve twice for a 4-0 lead. Rublev, who delivers his forehand with brutish force, 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 number three again at 5-5 with a yet another forehand winner and finished the job a game later to record a third straight win over Thiem.U.S. Open champion Thiem, runner-up to Tsitsipas in last year’s final here in London, now has a day off to shrug off the defeat and prepare for Saturday’s semi-final when he will face either world number one Novak Djokovic or Alexander Zverev. “It was difficult to keep the intensity like I had in the first two matches,” Thiem, who produced a masterful display to beat Nadal on Tuesday, told reporters. “When I’m not at 110% at this tournament there is no chance against any player, that’s what happened today.” Later on Thursday Nadal faces a crunch match against Tsitsipas with the winner joining Thiem in the semi-finals.