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.
"When I'm not at 110% at this tournament there is no chance against any player, that's what happened today". A bad game in 5-4 of the second affected it a little bit. I think I started to serve a little bit worse, but in general terms it has been a very positive match for me. I would maybe still have a chance to be in the semi-finals...
"It was not easy for Dominic but I think he is also focused now already on the semis so I wish him the best of luck".
Tsitsipas' record against Nadal now stands at 1-6, with his only victory coming, somewhat unexpectedly, on clay in Madrid last spring.
Tsitsipas was again under pressure in his next service game and this time he cracked, double-faulting on break point. "It's nearly impossible to beat him after losing the first set".
Just when it seemed likely he would canter to victory his level dipped and he dumped a forehand into the net to hand Thiem a break, smashing the ball away in frustration.
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 said the loss to Rublev was "not painful at all".
Later on, Thursday Nadal faces Tsitsipas with the victor joining Thiem in the semi-finals.
Dominic Thiem slumped to defeat against Andrey Rublev in a dead rubber at the ATP Finals on Thursday as reigning champion Stefanos Tsitsipas and Rafael Nadal prepared for a shootout to reach the semi-finals.
The Russian took advantage of an off day for his opponent to score a 6-2 7-5 victory, a fine way to end a year in which he has won a tour-leading five titles.
While the result was immaterial in terms of the future of the tournament, it still earned Rublev 200 ranking points and 153,000 USA dollars (approximately £114,000) in prize money. "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.
"So with the fact I was already qualified, in the back on my mind it was hard to keep the intensity alive".