But with the game lasting a succinct 60 minutes, there was little danger.
The Belgian fended off a fourth match point before Dimitrov finally sealed it when Goffin dumped a seemingly unmissable drop volley into the net. It was a very close match, which was predictable as Sock saved one match point to beat Dimitrov in 2015 Montreal, and four match points earlier this year in Indian Wells.
On the opposite side of the draw, fates was hung upon the result of Dominic Thiem's matchup with David Goffin.
But Goffin is made of sterner stuff.
Although Dimitrov - making his first appearance at this event in 2017 - broke straight back, Goffin raced into a 40-0 lead on his way to restoring his advantage by winning the next.
But Dimitrov will wake up this morning, not only presumably sharing a bed with Nicole Scherzinger but also knowing that he is the No 3 tennis player in the world in the new rankings.
"I have nothing to lose", Goffin said. He will face David Goffin for the second time this week, after that in the Round Robin the Bulgarian trashed him prevailing 6-0 6-2.
The season-ending extravaganza ATP Finals ends another memorable year which will be covered via our website www.skysports.com/tennis with live blogs, reports, reaction and expert analysis as the season reaches its climax. This is again the Roger Federer show.
The 19-time Grand Slam victor said he was disappointed to finish the year on this note and wished he could have played a more attacking tennis.
The opening game of the third set was a marathon 11 minutes, which included five break points, but Dimitrov held on.
After three consecutive breaks, the Belgian seventh seed was the first to hold his serve, forging ahead 3-1 and the match then settled back into a more predictable pattern.
But Goffin broke serve with a forehand victor in the second game of the second set and consolidated his advantage to take the match into a decider.
Goffin recovered from a set down to stun favourite Roger Federer on Saturday night, but he was second best in Sunday's final. He returned so well. On top of this, Novak Djokovic and Andy Murray both didn't even make it to the end of this year due to injuries, and although them coming back makes things even more interesting next year, I don't think things will ever return to normalcy with "the big four" at the top of men's tennis. "I'm hoping that it's going to be a tough match, and I'm trying everything to go through to the semis", he added.