Taiga Semikawa missed a chance to card only the sixth sub-60 round on the JGTO (since 1985) but still enjoyed a career-best 10-under-par 61 to take a two-shot lead after the opening round of the Tokai Classic on Thursday.
Seeking his second win of the season, Semikawa needed just one more birdie on the last two holes at Miyoshi Country Club's West Course to record the magical 59 but settled for a par-bogey finish instead.
Starting from the 10th tee, Semikawa delivered an electrifying performance, birdieing 11 out of 15 holes beginning from the 12th.
Still, his exceptional play earned him a slice of history as he set the tournament's lowest 18-hole score, one shot better than the nine-under-par 63 posted by four different players on the par-72 course.
Previous record holders include Y.E. Yang of South Korea (third round in 2018), Yoshinori Kaneko (fourth round in 1991), Masashi 'Jumbo' Ozaki (second round in 1986), and Yoshihisa Iwashita (second round in 1984).
Semikawa holds a two-shot lead over Taisei Shimizu. South Korea's Ryu Hyun-woo and Yuta Kinoshita trail by three shots after firing matching 64s.
Ryosuke Kinoshita sits in fifth with a 65, while defending champion Riki Kawamoto is tied for ninth place with a group of six players, each carding 67s.
The 22-year-old Semikawa credited his excellent score to his new mallet putter.
"It felt great today. I tried the mallet putter this week after missing the cut last week, and it really helped my game. It's been a while since I made a seven-meter putt, like the one on the 13th," said Semikawa, the Kansai Open winner earlier this season.
"The new putter simplified my approach. I'm beginning to think the mallet might be right for me."
When asked if he realised the potential record-breaking feat as he approached the final holes, Semikawa said, "Riki-kun (playing partner Kawamoto) brought it to my attention.
"He commented that 'it's already decided,' referring to the course record. Riki-kun is a source of encouragement. It's refreshing to play feeling this relaxed after so long."
Kawamoto, who also had a promising start with an eagle and three birdies against a single bogey, expressed admiration for Semikawa's performance.
"I didn't imagine the tournament record could go this low. Semikawa often excels on challenging courses. Watching him, it's as if he's playing on a completely different, simpler course. It made focusing on my own game quite challenging," Kawamoto remarked.
Following a strong start, Kawamoto is resolved to defend his title.
"I'm feeling great. If I maintain my focus and play my game, I believe I can continue to position myself well tomorrow. I'm committed to giving it my all," the determined champion stated.
Leading first round scores:
61: Taiga Semikawa;
63: Taisei Shimizu;
64: Ryu Hyun-woo (Kor), Yuta Kinoshita;
65: Ryosuke Kinoshita;
66: Mitsumasa Tamura, Ren Yonezawa, Takashi Ogiso;
67: Takahiro Hataji, Tomoyasu Sugiyama, Yuki Inamori, Takumi Kanaya, Riki Kawamoto, Koshiro Kaneko.