Winger Amanaki Lotoahea scored the only try of the game as Japan secured the 2017 Asia Rugby Championship with a 16-0 victory in Hong Kong on Saturday after recording a fourth win in as many matches.
On a wet day at the Hong Kong Football Club, the Brave Blossoms won their 25th title and 10th in a row since it became an annual tournament with an underwhelming performance that will do little to worry the 2019 Rugby World Cup host's opponents.
Japan were fielding a weakened side due to Super Rugby commitments for a majority of their big-name players but a plethora of handling errors by the favourites helped Hong Kong keep the scoreline down to a respectable total.
The visitors led 3-0 at halftime before Lotoahea scored in the 47th minute after he had been put clear by centre Kanta Shikao. Flyhalf Takuya Yamasawa kicked a successful conversion to go with his three penalties to complete the scoring.
The champions defeated Hong Kong in Tokyo last week after recording home-and-away victories over South Korea earlier in the three-team tournament.
At last week's draw for the 2019 Rugby World Cup, Japan were placed in Pool A alongside Ireland, Scotland and two yet-to-be determined qualifiers.
(Reporting by John O'Brien in Singapore; Editing by Toby Davis)