The 26-year-old claimed the biggest title of his career as he won an enthralling see-saw final 7-5 4-6 6-3 at London's O2 Arena.

The Bulgarian came through the tournament unbeaten and will end the year ranked third in the world, with his defeated opponent up to seventh.

"It has been a tremendous two weeks for me," said Dimitrov.

"It is such an honour to play here. 

"This week has been one of the best I have had.

"David is such a tremendous guy, forget the tennis. 

"He is one of the most improved players this past week and months. 

"It was an unbelievable effort. 

"I am very proud to play him in the final.

"I am lost for words."

Not since Spain's Alex Corretja, who won the season-ending title at his first attempt in 1998, has the occasion been marked by such a surprise victor.

Goffin will lick his wounds, content to have enjoyed a phenomenal week that saw him depose Roger Federer in the semi-finals.

But he has little time to rest as he must now try to help Belgium to a first ever Davis Cup victory against France next week.

"It was a special week for me," he said. 

"A week with a lot of emotion and a lot of fatigue. 

"Now I am feeling tired but it was an amazing week."

Dimitrov had thrashed Goffin for the loss of just two games only four days earlier in the group stage but the crowd were treated to a classic this time around.

It was in fact Goffin who made the early running and Dimitrov had to recover breaks of serve twice in the opening eight games.

Dimitrov moved ahead when he converted a fifth set point in the twelfth game.

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.

Goffin grabbed his chance in the next game with a forehand winner and confidently served out the set to force the game into a decider.

The final set ebbed and flowed, with Dimitrov fending off four break points in the first game before moving 4-2 up when Goffin sent a backhand long.

Dimitrov edged to the brink of victory, only for Goffin to serve his way back from 0-40 and three match points down.

The Belgian fended off a fourth match point before Dimitrov finally sealed it when Goffin dumped a seemingly unmissable drop volley into the net.

Finland's Henri Kontinen and Australian John Peers, the second seeds, retained their doubles title with a 6-4 6-2 win over top seeds Lukasz Kubot of Poland and Brazilian Marcelo Melo.