Mikumu Horikawa and Americans Ben Shelton and Eric Cole were among five players just a shot back at the Accordia Golf Narashino Country Club on the outskirts of Tokyo – the only PGA Tour event in Japan.

Cam Davis is the leading Australian in a tie for eighth at three-under, one better than Aaron Baddeley and two shots ahead of Min Woo Lee – who is trying to back up his wire-to-wire victory at the Macau Open on Sunday.

Adam Scott is even with the card after opening with a 70.

Morikawa has Japanese ties on his father's side, though he's unclear who his distant relatives might be in Japan. His mother's roots are in Hong Kong.

"There's obviously a little bit more meaning to this tournament for me," he said.

"But look, a win's a win, I'll take a win anywhere, right. I'm doing everything I can the next three days and kind of tonight to make sure I give myself the best opportunity to do that."

Japanese player Horikawa joked about looking up at the leaderboard and seeing a "kawa" on top – but that was Morikawa not Horikawa.

The suffix or prefix "kawa" means river in Japanese and appears in many Japanese family names and place names.

"So, oh, that's not me," Horikawa said. "Oh, I want to catch up with him."

Morikawa won the PGA Championship in 2020 and followed it with the Open, his quick fame putting him in demand abroad.

"Whenever my parents didn't want me to understand anything, they spoke in Japanese. It's been around me my whole life." – Xander Schauffele.

"It's been nice," he said.

"We've kind of been able to travel over here and play golf to just learn a little bit more and kind of reconnect with the culture and essentially my history."

The Zozo field is stacked with Japanese connections and many local players.

Xander Schauffele, three back after a 67, has maternal grandparents living in Tokyo. His mother, Ping Yi, has roots in Taiwan and grew up in Japan.

Schauffele's mother-in-law is also Japanese, and his wife is half Japanese and grew up in Japan's southern island of Okinawa.

Rickie Fowler's mother has Japanese roots and his grandfather, Yutaka Tanaka, is Japanese.

Kurt Kitayama's mother was born in Japan, and his father, Clifford, is Japanese-American.

Fowler and Kitayama each shot 71 on Thursday.

Schauffele's parents also spent time living in Tokyo. He said he was familiar with the language, but not fluent.

"I need a lot of help," the American said.

"The more time I spend here I pick up on phrases.

"Whenever my parents didn't want me to understand anything, they spoke in Japanese. It's been around me my whole life."