Tsitsipas emerged victorious in three sets in the 2019 meeting and while this was a similarly well-contested match, it was Thiem who came out on top 7-6 (7-5) 4-6 6-3 this time.
Thiem took the first set in a tiebreaker having generally looked the more threatening of the two, and although Tsitsipas fought back well in the second, the Austrian got the job done impressively to give the world number three a satisfying start that he feels could be vital.
Speaking on court afterwards, Thiem said: "I experienced in the past four years how important it is to have a good start in this tournament, to ideally win the first match. I am very happy that I did it."
Tsitsipas was put under pressure on several occasions in the first set, forced to save three break points as he held firm to take Thiem into a tiebreak.
He then looked in with a great chance of taking control of the match when going 4-1 up, but he lost his serve to see his lead quickly cut to 5-4, the first of four successive points rattled off by Thiem that sealed the set.
Tsitsipas came out fighting in the second, however, taking Thiem to deuce in the latter's opening service game before then breaking at the second time of asking. That game proved decisive too, as he took the set 6-4.
Yet any momentum from that soon vanished, Thiem quickly finding himself 3-0 up in the decider having dropped just three points as Tsitsipas' sole opportunity to break back went begging as he trailed 4-1.
The rest of the contest went with serve, Thiem getting his campaign in Group London 2020 off to a winning start, with Rafael Nadal and Andrey Rublev the other two in the pool.