The win was more good news for de Minaur, who had earlier been crowned the ATP World Tour's Newcomer of the Year.
The pair, neither of whom qualified for the inaugural event past year, have been the most exciting breakthrough talents of 2018 so it was fitting the final pitted one against the other.
Tsitsipas - whose looks have been compared to legendary Swede Bjorn Borg - has an aesthetically pleasing one-handed backhand and more natural power than his opponent, while possessing plenty of fight of his own. He served at 72% and had 10 aces, saving all five break points he faced to keep the pressure on Munar who gave his best to stay in touch with the better-ranked rival and reach the fifth set, defending 13 out of 17 break points he faced and saving the first five match points he had to play against.
World No.31 De Minaur, the only teenager in the elite season-ending event for the best 21-and-under players, saved two match points at 3-2 down in the fourth set in the shortened format but his resistance ran out in the tiebreaker.
He said he didn't know how he recovered from those match points.
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"I'm going to have to play differently than today", he said post-match.
De Minaur added: 'It's been an unbelievable year. It's a shame it couldn't finish with a win but I couldn't be prouder. I was mentally very strong and that proved in the tiebreak in the last set. Congratulations to Stef and his team for an fantastic year and an wonderful week'.
He said winning the final would be "the cherry on top of an unbelievable season for me".
Rublev eased past Italian wild card Liam Caruana 4-3 (9-7), 4-1, 4-2 to book his passage after losing to de Minaur on Wednesday, with Munar beating American Frances Tiafoe 4-1, 4-3 (7-3), 4-1 to seal the final berth.