Grigor Dimitrov marks ATP Finals debut with win over Dominic Thiem

Dimitrov surrendered a one-set lead at London's O2 Arena and then needed two chances to serve for victory in the decider before edging past the talented Thiem 6-3 5-7 7-5.

With Andy Murray away injured, Roger Federer and Rafael Nadal are the stand-out attractions at this week's tournament but there may be few contests as entertaining as this one, lasting two hours and 19 minutes.

Nadal opens his campaign against David Goffin later on Monday but if the Spaniard's creaking knee proves a burden, Dimitrov could even be a dark horse to top the group.

To do so, he will have to calm his nerves. The 26-year-old is the first Bulgarian qualifier here in the competition's 48-year history and he admitted on court afterwards that he had struggled to handle the pressure.

"I'm not going to lie, I was pretty nervous in my first match out here," Dimitrov said.

"It's not the same as practising on this court, you feel the weight on your shoulders, in a positive way of course. I'm just very grateful to win in that manner. It's not easy playing here for the first time."

Ranked a career-high sixth in the world, Dimitrov took a break midway through the opening set and served out but Thiem levelled when his opponent wavered at the end of the second.

A shanked forehand wide gave Thiem a set-clinching break at 6-5 but Dimitrov again pulled ahead in the third, when a sensational drop-volley put him a break and 4-3 up.

Serving for the match at 5-4, however, he wobbled again as a framed backhand beyond the baseline allowed Thiem a reprieve.

But the Austrian, perhaps also affected by the jitters, failed to consolidate as two consecutive double faults allowed Dimitrov a 6-5 advantage and a second chance to serve out.

Even with two match points, Dimitrov threatened to choke again as he spurned both, one with a double fault of his own. He finally converted a third, however, when a Thiem backhand landed long.