Japan's Shohei Ohtani hit his second home run of the World Baseball Classic on Saturday and said his team's nail-biting 8-6 win over South Korea would bring the defending champions closer together.

Los Angeles Dodgers superstar Ohtani smashed the ball into the Tokyo Dome stands for the second game running, but Japan were pushed to the limit by the tenacious Koreans.

Japan found themselves three runs down after the first inning but Ohtani said having to battle back into the game would serve them well for the rest of the tournament.

"When you manage to win these kinds of games it really brings the team together and raises your overall level as a group," said the 31-year-old, who also hit a home run in Japan's opening win over Taiwan.

"Coming out on top today was huge and I think every single guy on this team is a great player."

Seiya Suzuki hit two home runs and Masataka Yoshida bagged one more for Japan, who made it two wins out of two in Pool C.

South Korea suffered their first loss, after starting their campaign with a win over the Czech Republic.

The Koreans made a stunning start with three runs in the first inning but Japan hit straight back through Suzuki's two-run homer in the bottom of the first.

The shot cut South Korea's lead to just one run and Ohtani said it helped Japan "settle into the flow of the game".

"We had given up three runs early, so being able to cut it down to a one-run game as quickly as that was huge," he said.

Momentum shift

Ohtani tied the game when he sent a mammoth shot into the stands in the third inning.

Japan went in front with two more solo home runs in the same inning from Yoshida and Suzuki.

"I think the biggest thing is that no one gets flustered," said Ohtani.

"Whether we're in a jam or we have a scoring chance, everyone is able to focus on their own play."

Just when Japan looked like running away with the game, South Korea hauled them back as Park Dong-won hit a two-run home run to tie the game in the fourth inning.

Japan edged ahead in the seventh inning when reliever Kim Young-kyu got himself into trouble and the Koreans could not recover.

"We gave up three runs at the start and if we hadn't scored at the bottom of the first, the momentum of the game would have been with our opponents," said Japan manager Hirokazu Ibata.

Japan starting pitcher Yusei Kikuchi, who went to the same high school as Ohtani, gave up three runs in three innings before leaving the game.

Japan play Australia in their next game on Sunday.

South Korea face Taiwan earlier in the day with a place in the quarter-finals still up for grabs.

"We gave up four home runs in the first three innings today and that was not in our game plan," said manager Ryu Ji-hyun.

In the other game in Pool C, Taiwan routed the Czech Republic 14-0 to pick up their first win of the tournament.