American Brendan Steele took the lead with a 6-under 64 in Thursday's opening round of the Zozo Championship at Narashino Country Club outside Tokyo.
Players from the United States dominated the top of the leaderboard on the opening day, with Adam Schenk trailing Steele by a stroke, ahead of Sam Ryder, Matthew NeSmith and Keegan Bradley tied for third at 66.
Kazuki Higa leads the Japanese contingent after firing a 3-under 67 that left him tied for sixth, while defending champion Hideki Matsuyama made a shaky start in his bid to become the tournament's first two-time winner, carding 71 to finish 1-over in a tie for 41st.
Steele, the runner-up last year to Matsuyama, birdied the final four holes following his solitary bogey on the par-5 14th, with six of his seven birdies for the round coming on the back nine.
Teeing off on the back nine, Matsuyama carded two birdies against three bogeys as he showed signs of the back trouble that had affected him ahead of the tournament.
The PGA tournament through Sunday is the fourth edition of the Zozo Championship and the third staged in Japan, after the 2020 event was moved to the Sherwood Country Club outside Los Angeles because of the coronavirus.