The result saw the world No3 exact some revenge on his Greek opponent, who was the victor when the pair met in the final of least year’s edition of the tournament in London.
There was a strange atmosphere in the O2 Arena for the opening clash, but neither the defending champion nor this year’s US Open winner struggled for motivation.
There were fine serving displays on both sides, with the two players also showing off a variety of skills in competitive rallies that often ended with deft play at the net.
The first set featured a number of holds to love, with neither man able to find a break of serve, leaving a tiebreak to separate the pair.
That first-set decider represented a missed opportunity for Tsitsipas, who gave up a 4-1 lead as Thiem fought back to make it 5-5. The Austrian then sealed the tiebreak when a Tsitsipas lob drifted long, moments after the Greek had failed to put enough force behind a smash that would have saved set point.
The 22-year-old was wasteful again in the first game of the second set, failing to capitalise on a 0-30 lead on Thiem’s serve, but he wrong-footed his opponent two games later to seal a break of serve – the first of the match – with a backhand passing shot winner down the line.
Both men impressed at various moments throughout the remainder of the set, but Thiem was unable to find what would have been a crucial break, and Tsitsipas ultimately served out the frame at 5-4.
Thiem responded perfectly, however, breaking the Greek with a dropshot winner for a 2-0 lead in the deciding set. A clinical hold of serve followed and the one-time Grand Slam champion increased the deficit over his friend.
At 3-1, Thiem faced some adversity as he struggled to hold – missing numerous chances to convert game point – but he ultimately got the job done to move to within two games of victory.
While Tsitsipas fought valiantly to remain in the match, he was unable to close the gap and Thiem stepped up to serve out the match at 5-3.
Although the Greek was able to save one match point, Thiem’s serving proved too much and he wrapped up the win after two hours and 18 minutes on court.
World No2 Rafael Nadal and Andrey Rublev are next up in Group London 2020 as they go head-to-head on Sunday evening.
This weekend get a £10 free bet with Betfair, when you bet £10 on a Same Game Multi on the Premier League. Terms: Min £10 Same Game Multi bet on any EPL match this Fri – Sun. Free bet valid for 72 hours, awarded at bet settlement. Excludes cashed out bets. T&Cs apply.