Dimitrov made an impressive start to the tie at the O2 Arena in London, as he broke his Austrian opponent on route to winning the first set.

Having lost the opener 6-3, Thiem began to find his rhythm in a tightly contest second set.

He slowly began to carve out opportunities on Dimitrov’s serve, forcing his first break point as the set reached its conclusion, with the subsequent break helping him to force a decider.

Dimitrov recovered impressive to break in the third, but he failed to serve out the match at the first time of asking.

Two doubles faults from Thiem allowed the Bulgarian to re-establish his lead in the set, with the sixth seed eventually completing at 6-3, 5-7, 7-5 victory.

“It's never easy to come out here and play for the first time,” said Dimitrov.

“I'm super excited to be out here.

“Every match I want to win 100 per cent for myself and follow what I've been working on.

“Things seem to be going the right way so far.”

The result placed Dimitrov at the top of the Pete Sampras group at the end of season tournament.

He was later joined by Belgium’s David Goffin, after he won a tight match against Rafael Nadal of Spain.

Nadal was presented a trophy yesterday after ending the year as world number one, yesterday.

There had been doubts over his fitness before the tournament, with the Spaniard admitting his preparations were “not perfect” due to a knee injury.

Goffin took advantage on an ailing Nadal to win the opening set on a tie-break, before the Spaniard hit back to do the same in the second, after his opponent passed up four match points.

It proved only a small respite for Nadal, as he was broken twice at the start of the decider.

Despite breaking back, he proved unable to complete a comeback as Goffin triumphed 7-6, 6-7, 6-4 for arguably the biggest win of his career.

Switzerland’s Roger Federer and Germany’s Alexander Zverev earned victories in the Boris Becker group yesterday.

The pair will meet tomorrow, after Croatia’s Marin Cilic takes on American Jack Sock.