Japan began the inaugural Asia Rugby Championship just as it left off the old Asian 5 Nations with a bonus-point win Saturday. But it was hardly a performance that will have worried South Africa, Scotland, Samoa and even the United States, its opponents at this year's Rugby World Cup.

The Brave Blossoms beat South Korea 56-30 at Namdong Asiad Rugby Field, but it was an error-strewn performance from Eddie Jones' team.

"We were a bit rusty both individually and as a team, and sloppy for most parts of the game," Jones said shortly after the final whistle. "Korea played well for the first 30 minutes and we gave them some points which got their spirits up. They were physical and tackled well."

Handling errors prevented Japan from getting on the board early on and after an exchange of penalties between Ayumu Goromaru and Oh Youn-hyung, it was the hosts who crossed twice in the space of four minutes through fullback Jang Seong-min, aided and abetted by the equally impressive Lee Myung-jun.

South Korea's 17-3 lead was short-lived. Tries by Hayden Hopgood and debutant Chihito Matsui and a penalty try pulled Japan ahead 22-20 at the break.

"The players really gave 100 percent in the first half," said Korea coach Chung Hyung-suk.

The second half saw the Brave Blossoms step up a gear as the Koreans tired and there were further tries for Japan's most impressive player Karne Hesketh, Yu Tamura, Yoshikazu Fujita, Ryu Koliniasi Holani, Justin Ives and Hopgood.

Japan's "sloppy" performance was best summed up by the poor goalkicking of Goromaru — who kicked just four conversions from nine attempts — and a number of passes, particularly from Yu Tamura and Harumichi Tatekawa, that went nowhere near where they were intended.

"The problem was the players weren't looking at the defense," Jones said of his side's inability to score more tries and their propensity to give the ball away, while he said individual errors allowed Kim Nam-uk to cross in the second half.

"Before the game I thought we would either play really well for 20 minutes or not play well," he said. "And unfortunately it was the second."