Australia's Paul Sheehan, who won two tour events last year, shot a 2-under-par 68 Thursday to grab a share of the lead with four others after the first round of the Mitsubishi Diamond Cup.
Sheehan made seven birdies and five bogeys on an exceptionally tough layout for a domestic tournament on a day when relative unknowns Yutaka Horinouchi, Azuma Yano and Sushi Ishigaki finished atop the leaderboard along with veteran American Peter Teravainen.
Keiichiro Fukabori, whose six career titles include the 2003 Japan Open, and Masaya Tomida had 69s and are one stroke behind the joint leaders at Higashi Hirono Golf Club.
Shingo Katayama and Toshimitsu Izawa are among five players who matched par for the day.
Hiroyuki Fujita, winner of last week's Munsingwear Open KSB Cup, opened with a 73.
Defending champion Tetsuji Hiratsuka struggled to a 78, falling victim to the narrow fairways and fast greens.