The match between two players, who will be among the shortlist of favourites at next month's Australian Open, fully lived up to the expectations.
Nadal took a service-break lead at 5-4, but faltered when trying to serve out the first set and then lost the tiebreaker on Saturday, reports Efe news.
The second set nearly came down to a tiebreaker as well, but Nadal won six out of eight games to capture the second set 7-5 and take a 4-2 lead in the decider.
The 21-year-old Tsitsipas, who looks set to challenge the dominance of Nadal, Serbia's Novak Djokovic and Switzerland's Roger Federer in 2020, was not done yet though.
The world No. 6 showed his return-game prowess in breaking back to even the set, although the 19-time Grand Slam champion finally pulled away in the match-deciding tiebreaker to capture a record fifth Abu Dhabi title.
It was the second straight down-to-the wire contest between Tsitsipas and Nadal, who edged the rising Greek star 6-7 (4-7), 6-4, 7-5 last month in the round-robin phase of the ATP Finals, men's tennis' elite, eight-man, season-ending tournament.
Tsitsipas went on to win that event the biggest title of his career thus far by defeating Federer in straight sets in the semifinals and Austria's Dominic Thiem in three sets in the final.
Earlier, Djokovic topped Russia's Karen Khachanov 7-5, 6-3 in the third-place match.
Nadal, Federer, Djokovic and Tsitsipas will arguably be the top four favorites at next month's Australian Open, the first Grand Slam event on the 2020 tennis calendar.
( With inputs from IANS )