Tokyo (AFP) - Shohei Ohtani blasted a home run to ignite Japan’s World Baseball Classic campaign as the defending champions thrashed Taiwan 13-0 in their tournament opener in Tokyo on Friday.

Los Angeles Dodgers superstar Ohtani’s grand slam set the tone as Japan scored 10 runs in the second inning alone in front of around 42,000 fans at the Tokyo Dome.

Their dominance meant the game was cut short after seven innings under the so-called mercy rule.

“Everyone stayed focused after my home run and that gave us a good start,” said Ohtani.

“It was our first game so everyone was a little uptight, but we wanted to be aggressive and attack the ball.”

The result gave Japan a dream start to the tournament as they go in search of a record-extending fourth title.

Taiwan, who were backed by a large and noisy travelling support, lost their second straight game following Thursday’s defeat to Australia.

An expectant Tokyo crowd that included Puerto Rican music star Bad Bunny and American actor Timothee Chalamet packed the stands for their first glimpse of Ohtani at this year’s tournament.

Japan manager Hirokazu Ibata said having the 31-year-old in his team “helps us a lot”.

“It wasn’t only Ohtani because after his grand slam we scored a lot of runs,” said Ibata.

“We’ll try to keep this going for the next three games.”

Ohtani hit a double off the first pitch of the game but Japan were unable to get on the scoreboard as Taiwan starting pitcher Cheng Hao-chun saw off the danger.

There was nothing Cheng could do when Ohtani smacked a grand slam home run in his next at-bat to put Japan up by four runs.

“Watching Shohei’s pre-game routine impressed me,” said Ibata.

“He knows how to get ready for the big games.”

- ‘Best in the world’ -

Japan’s batters were not finished there and they went on to rack up six more runs before the second inning was over.

They added three more in the third inning as things went from bad to worse for Taiwan.

Taiwan manager Tseng Hao-jiu said his team could not live with Ohtani’s quality.

“He’s the best in the world, I can’t describe how good he is,” said Tseng.

“With one swing, he changed the entire game.”

Japan could not add to their score but the fact that they were ahead by 10 runs or more at the end of the seventh inning meant the game ended two innings early.

Japan starting pitcher Yoshinobu Yamamoto left the game in the third inning.

Yamamoto, last season’s World Series MVP with the Dodgers, started well before tiring and allowing two Taiwanese batters on base.

“After we scored a lot of runs I was trying to focus but my command wasn’t as good as I expected,” said Yamamoto.

“I have little things to fix but overall we won tonight and that meant everything.”

Japan play their next game against South Korea on Sunday.

Australia beat the Czech Republic 5-1 earlier on Friday in Pool C.