Tsitsipas, 20, who had rocketed up the rankings to No. 16 heading into Stockholm, made up for losing two finals this year by outplaying Gulbis in straight sets.
It was a clinical display by Tsitsipas, who converted the two break points that came his way while offering precious little chances for qualifier Gulbis to threaten.
Tsitsipas began the year just inside the world's top 100 with only four Tour-level wins to his name but has matured into one of the sport's most dangerous newcomers.
In August at the Rogers Cup in Toronto, he became the youngest player to beat four top-10 opponents at a single event since the ATP World Tour began in 1990, eventually losing to Rafael Nadal in the final.
A few months earlier in Barcelona, he became the first Greek man to reach an ATP Final since 1973. He has already qualified for the ATP Next Gen Finals in Milan next month.