Collin Morikawa shot a six-under 64 to lead the Zozo Championship after the first round of the PGA Tour event at Accordia Golf Narashino Country Club.
Home player Mikumu Horikawa and victorious Team Europe Ryder Cup member Nicolai Hojgaard were among five players just a shot back at the course on the outskirts of Tokyo, the only tournament on the North American circuit which is held in Japan.
Morikawa has Japanese ties on his father's side, though he is unclear who his distant relatives might be in Japan. Regardless, he was delighted with his start as he aims for a first PGA Tour win since the Open two years ago.
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"There's obviously a little bit more meaning to this tournament for me," Morikawa 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.
"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."
Japanese player Horikawa joked about looking up at the leaderboard and seeing a 'kawa' on top - but that was Morikawa rather than him.
"So oh, that's not me," Horikawa said. "Oh, I want to catch up with him."
The Zozo Championship field is stacked with Japanese connections and many local players.
Xander Schauffele, three back after a 67, has maternal grandparents living in Tokyo and his mother, Ping Yi, has roots in Taiwan and grew up in Japan.
His 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 in the opening round.
Schauffele's parents also lived for a time in Tokyo. He said he is familiar with the language, but not fluent.
"I need a lot of help," Schauffele 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."
Coverage of the Zozo Championship continues on Sky Sports Golf from 4am and Sky Sports Main Event from 4.30am on Friday. Also stream with NOW.