Hirotoki Onozawa's try four minutes from the end secured Japan a 34-23 victory over Romania on Saturday in the opener of their four-match tour.
Both sides conceded penalty tries in a three-minute span, Romania deliberately collapsing a maul, and Japan collapsing a scrum, to leave Japan leading by one with eight minutes to go.
But then Fumiaki Tanaka set up Onozawa for a converted try, and there was enough time left for Ayumu Goromaru to bang over his fifth penalty in a personal 19-point haul at the match in Bucharest.
Japan struggled to handle Romania's strength in the scrums and breakdowns, but enjoyed the edge in ball and territory.
The visitors led 17-9 at the break, with a late try by Takashi Kikutani, who capped a flowing move.
On the hour, Romania closed to within a point when pressure on a Japan scrum put-in ended with Romania winger Madalin Lemnaru racing from halfway for a converted try.