Tonga scored four tries on Saturday to beat Japan 27-17 in the opening match of the Pacific Nations Cup at Nippatsu Mitsuzawa Stadium in Yokohama.
Two early tries by Fetu'u Vainikolo and a kick by Fangatapu Apikotoa saw Tonga take a 12-0 lead.
Takeshi Kizu ran in a try in the 20th minute to give the hosts some life but a try by Will Helu and a penalty and conversion by Apikotoa allowed Tongo to head into the break with a 22-5 lead.
Male Sa'u scored Japan's second try a minute after the break but Eddie Aholelei grabbed Tonga's fourth minutes later to complete the scoring for the visitors.
Hendrik Tui scored Japan's third try in the 62nd minute, converted by Ayumu Goromaru, but Tonga's defense maintained the 10-point lead.