But in a huge turnaround of furtunes, Dimitrov responded in unerring fashion with a flawless 6-0 scoreline in 22 minutes to set up a deciding set shoot-out. He pushed, chanced the angles, flirted with the lines, and in the second game of the second set, he threaded the needle in his first breakpoint opportunity of the match and then swept to a 3-0 lead.
The second game of the second set was to prove a turning point as Goffin, beaten 6-2 6-1 by Federer in Basel last month, broke the Swiss's serve with a forehand victor and then consolidated his lead to take the match into a decider.
Federer, as the 14-time semifinalist against Goffin making his semifinal debut, was the one playing with everything to lose.
Ahead of Saturday's ATP Finals semifinal, David Goffin said that he would "try something, something different, something that I've never done in the past" in an attempt to try to overhaul Roger Federer. The match will be the fifth time the two play against each other in 2017: Dimitrov won in the quarterfinals of the Australian Open, the Sofia Open final and earlier this week in the ATP finals round robin - a forceful demolition with a matching scoreline 6-0, 6-2 - while Goffin's only success came in Rotterdam.
"It has been one of the best weeks I have ever had", he said.
The season-ending extravaganza ATP Finals at London's O2 ends another memorable year which will be covered via our website www.skysports.com/tennis with live blogs and updates as the season reaches its climax.
Federer was too good for Nadal in the final. Image Getty
"It was the only game I didn't serve well". "It was a special week for me - a week with a lot of emotion, a lot of fatigue, but it was fantastic", said the player who became one of only six men to have beaten Federer and Nadal in the same tournament. In that third set I was just trying to get that break. He completed the job on serve to set up a meeting with Goffin on Sunday.
Play continued with serve, but the early break allowed Goffin to serve for and claim the second set 6-3.
Goffin, 26, landed just 42 percent of first serves in the first set and made 20 unforced errors, struggling to find the bite and consistency he had enjoyed in beating Federer.
But the psychological advantage Goffin's netted forehand gave Dimitrov lasted only until mid-way through the second set, when the less fancied of the two players broke and then closed out the set to level the score. I was very composed and didn't let negative thoughts come to my head.
Dimitrov also played tribute to his girlfriend and popstar Nicole Scherzinger afterward for her support. But this time, instead of seeing a fiery Sock comeback, Dimitrov stormed to a 6-0 second set victory, losing just nine points.