The Belgian needed 84 minutes to beat Frenchman Mannarino 6-3, 7-5 for his first trophy at an ATP World Tour 500-level tournament and pocketed $336,900 in prize money and 500 Emirates ATP Rankings points.
In the opening set, Mannarino was under pressure in the second game when he was forced to save two break points on serve, but two games later the 26-year-old Goffin broke to lead 3-1 and never looked back to claim the set 6-3, only dropping four of his 25 service points on offer.
The second set went with serve until Goffin was broken to trail 2-4 but Mannarino failed not make his advantage count and was broken right back a game later for the Belgian to hold and level things at 4-4.
Goffin upped his intensity and was rewarded in the 11th game when he broke his opponent’s serve to lead 6-5 and served out the set and match to love, winning it 7-5.
The win in Tokyo was Goffin’s fourth career title and second of the season after his ATP 250 Shenzhen Open triumph last Sunday.
“I’ve been serving well for a few weeks,” Goffin said afterwards. “My second serve is really effective; my opponents don’t attack me, so I’m always ready to play the second shot.”