Dimitrov, who had a 100 per cent record in the group matches, asserted himself at the business end of the set and piled on the pressure when Goffin served at 5-6.
Goffin managed only two games against Dimitrov when they met last week in group play but the world number eight, who claimed a rare double of beating both Nadal and Federer this week, was a different proposition this time.
"I proved to myself that I'm in the right place, and I deserve to be here in this tournament".
Grigor Dimitrov consoles David Goffin after the final. I let him back into the game. "I'm just going to focus on what I can do and play hopefully the same game". He opened the second set with fight; holding another impressive service game before breaking Federer and then holding his second service game to love. Four break points for Thiem in the sixth, but a string of wild backhands allowed Goffin to claim the game before Goffin closed in on the final set 6-1.
"I think I've had good results in the past, but now I need to be even more consistent on those kind of events and in the same time raise up my level on occasions like this".
Goffin saved three match points to ask Dimitrov the serve it out, but he kept his composure to seal a famous win on his fifth match point, although he was given a helping hand as the Belgian dumped a simple-looking volley into the net.
Grigor Dimitrov had already qualified for Saturday's ATP Finals semifinal when he stepped out onto court on Friday, but that didn't prevent him from blowing Pablo Carreno Busta off the court with a crushing 6-1, 6-1 victory.
"It was a tough game [at 2-3] and I was a little bit exhausted in the third".
Dimitrov, whose title at The O2 joins previous victories in Cincinnati, Sofia and Brisbane, is still without a Grand Slam title and he acknowledged "there is a lot to be done" as he aims to make further strides in the game. In the second, I had some opportunities to come back, to break back, but he was really solid. "Somehow after the 3-0, I lost it until the end".
It was not the grand slam title he wants most but the next best thing and it felt like a breakthrough moment for a player widely perceived as one of the game's under-achievers. He broke into the top 10 for the first time in February and reached a career high No. 8-ranking earlier in November. "This has always been, again, a dream of mine".