25 unanswered second-half points saw Japan shock Canada in Burnaby to record their eighth successive victory on Saturday.
The Brave Blossoms defeated an under-strength Samoa last month, but looked well-beaten as the hosts raced to a 25-9 half-time lead through tries from John Moonlight, Ciaran Hearn and Taylor Paris, with James Pritchard converting two of the three scores and adding a brace of penalties.
Back came Japan after the break, however, with full-back Ayumu Goromaru failing to convert Yoshikazu Fujita's close-range try, but adding his fourth penalty of the night soon after.
Yu Tamura was next to cross for the Brave Blossoms with a scything midfield burst and finish just after the hour mark, Goromaru's conversion cutting the gap to a solitary point at 25-24.
Japan finally took the lead with Canada shell-shocked Hendrik Tui powered home, Goromaru adding the extras to ensure a superb opening Pacific Nations Cup win for the visitors.
Tries: Moonlight, Hearn, Paris
Cons: Pritchard 2
Pens: Pritchard 2
Tries: Fujita, Tamura, Tui
Cons: Goromaru 2
Canada: 15 James Pritchard, 14 Jeff Hassler, 13 Ciaran Hearn, 12 Nick Blevins, 11 Taylor Paris, 10 Harry Jones, 9 Gordon McRorie, 8 Tyler Ardron (capt), 7 John Moonlight, 6 Jebb Sinclair, 5 Jamie Cudmore, 4 Tyler Hotson, 3 Jason Marshall, 2 Ray Barkwill, 1 Hubert Buydens.
Replacements: 16 Andrew Tiedemann, 17 Aaron Carpenter, 18 Jake Ilnicki, 19 Jon Phelan, 20 Adam Kleeberger, 21 Phil Mack, 22 Connor Braid, 23 DTH van der Merwe.
Japan: 15 Ayumu Goromaru, 14 Yoshikazu Fujita, 13 Male Sa'u, 12 Yu Tamura, 11 Akihito Yamada, 10 Harumichi Tatekawa, 9 Fumiaki Tanaka, 8 Ryu Koliniasi Holani, 7 Michael Leitch (capt), 6 Justin Ives, 5 Luke Thompson, 4 Hitoshi Ono, 3 Kensuke Hatakeyama, 2 Shota Horie, 1 Masataka Mikami.
Replacements: 16. Hisateru Hirashima, 17 Takeshi Kizu, 18 Hiroshi Yamashita, 19 Shoji Ito, 20 Shinya Makabe, 21 Hendrik Tui, 22 Atsushi Hiwasa, 23 Toshiaki Hirose.
Referee: Leighton Hodges (Wales)
Assistant referees: Greg Garner (England), Nick Ricono (USA)