Grigor Dimitrov has recorded a three-set victory over Dominic Thiem in his first-ever match at the ATP World Tour Finals.
The 26-year-old has just moved up to a career-high world ranking of sixth place, and the Bulgarian has marked that achievement with a 6-3 5-7 7-5 triumph over Thiem at London's O2 Arena.
Dimitrov has failed to follow up his semi-final appearance at the Australian Open at the start of 2017, but the 26-year-old will be confident of reaching the last four of the end-of-season tournament after outlasting Thiem.
One break of serve was enough to take the opening set, but Thiem kept his composure to record the solitary break during the second to take the contest into a decider.
The third set was a tense affair but after Dimitrov failed to serve out the match at the first opportunity, two double faults from Thiem let Dimitrov back in to finally get over the line in two hours and 21 minutes.
Rafael Nadal and David Goffin - the other two players in the Pete Sampras Group - meet on Monday evening.
