The Swiss on Saturday was shocked by Belgian tennis player Goffin when he came back into the match to turn it in his favour and win 2-6, 6-3, 6-4 at the O2 Arena in London.
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.
Having become the sixth player to beat Nadal and Federer at the same tournament - the latter from a set down in the semifinals - Goffin had every reason to be confident after drawing level. "So when my body's allowing me to do this kind of preparation, I feel I already have an advantage over any other player". He played one very good match here, (and) one very bad match.
"Now I'm feeling exhausted, but it was an unbelievable week".
Dimitrov, playing the season finale for the first time, joins Group Boris Becker victor Roger Federer as the only unbeaten singles players, and the Bulgarian will fight for the champion berth against American Jack Sock on Saturday.
"I was in my match which was the important thing".
Dimitrov made the breakthrough after taking his second break point chance with an aggressive forehand in the eighth game.
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After five breaks of serve in the first set, the second was a much tighter affair, with Dimitrov missing out on a potentially decisive break in game six after a Hawkeye challenge. I knew what to expect. "I proved to myself that I can do it".
Discussing his performance in London, Goffin - who lost 6-0 6-2 to Dimitrov when they met earlier in the week - said: "It was a special week for me".
Dimitrov moved ahead when he converted a fifth set point in the twelfth game.
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.
"I think after this week I'm a better player mentally", said Goffin, who ends the season at a career-high No. 7 ranking. "He was really solid". "Of course, one of my main goals is to win a Grand Slam tournament".
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It was too close to call but two Sock double faults helped Dimitrov break for 5-3. "This has always been, again, a dream of mine".