Japan made sure of their sixth straight HSBC Asian 5 Nations title when they beat South Korea 64-5 at the Prince Chichibu Memorial Rugby Ground on Saturday.
Takashi Kikutani's try in the 23rd minute -- Japan's fourth -- brought up the bonus point Japan needed to ensure they cannot be overtaken in the standings even though they still have a game to play.
"We've got one game left but we are the champs so we have completed the first challenge of the season," said Japan coach Eddie Jones.
"I am very pleased with today's performance. It was a good first 40 minutes and although we got a little bit tired in the second half and were a bit flat, we finished well."
Kikutani added a second try to take him to 28, the most by a forward in test-match rugby, but it was Japan's young backs that dominated the rest of the scoring.
Kenki Fukuoka grabbed a brace and there were five-pointers for Yoshikazu Fujita, Kosei Ono, Male Sa'u and Ayumu Goromaru with Hendrik Tui and a penalty try ensuring the forwards' hard work was rewarded.
"The Japan players were quicker than we expected and we just couldn't cope early on," said Korean captain Park Soon Chai.
On a glorious spring day in the nation's capital, flyhalf Ono gave Japan the ideal start going over with just 90 seconds on the clock.
Fukuoka showed great speed off the mark to score five minutes later when he was put away in the narrowest of gaps by Fujita, before the 20-year-old added a second three minutes later.
A great steal by the Japan pack close to their own line allowed Atsushi Hiwasa to launch a counter-attack and Fukuoka's speed did the rest. Goromaru added the extras as Japan led 21-0.
The Korean backs occasionally looked dangerous but they were generally starved of the ball in the first half and Kikutani's brace simply reinforced the dominance of the Japan pack, for whom Michael Broadhurst was outstanding.
The captain's first came through a rolling maul and his second followed a strong run close to the point of breakdown as Japan made the most of some quick recycled ball.
Fujita crossed four minutes before the break after the Japan backs transferred the ball quickly to create an overlap following another good break by Broadhurst as Japan led 40-0 at halftime.
With the game and title assured, the second half ended up being a scrappy affair.
Japan extended their lead through tries by Tui, a penalty try and Goromaru (who finished the day with seven conversions to his name) before the Koreans became the first team to score against Japan this year when Oh Youn Hyung went over in the 77th minute.
Sa'u, however, ensured the day ended on a high for the hosts, crossing for what Jones described as a "text-book try" as the final hooter sounded.
"The first half was fantastic so why do you want to talk about the second half when we had the game won," Jones told reporters after the game. "We could have gone out 10 minutes late for the second half and let Korea play and still won the game."