In a photo finish to the tournament, which was jointly sanctioned with the Asian Tour, Imahira prevailed by one shot on eight-under for the tournament thanks to a rock-solid finish of pars down the closing stretch, while his rivals were dropping shots.

He closed with a two-under-par 68 with his compatriots Kosuke Suzuki, an amateur, Hiroshi Iwata, Kaito Onishi, and Yuto Katsuragawa all in second place.

Suzuki came charging out of the pack with a 63 – thanks to a brilliant back nine of five-under-par 30 – Iwata shot 68, while Onishi, who chipped in for birdie on 18, and Katsuragawa both carded 70s.

Imahira’s win also earned him a place in the elite field for The Open at St. Andrews in July – an event he has played in twice before.

The 29-year-old started the day one behind overnight leaders Onishi, Katsuragawa, Japan’s Ryuko Tokimatsu and New Zealander Ben Campbell but finished first helped by a brave back nine made up of eight pars and a birdie, on the par-5 15th.

Kiwi Ben Campbell didn't have his best stuff on Sunday when chasing victory. PHOTO: Andy Cheung/Getty Images.

It was a different story for Iwata, Onishi and Katsuragawa on the homeward nine as they dropped shots at critical moments. Onishi and Katsuragawa, in particular, both made double bogeys, on 13 and 15 respectively, while the later made a costly bogey on 17 which opened the door for Imahira.

Suzuki, just 21 years old, was the only player who got to grips with the back nine – he made three birdies in a row from the 11th and an eagle on 15 – but having started the day seven off the lead the gap proved too big to close.

“I am really happy with this victory. I haven’t really performed well this year, so I’m glad I am able to win early,” said Imahira, who won the JGTO money list title in 2018 and 2019 and whose last victory was the 2021 Fujisankei Classic.

“The Open was my goal at the start of this season. My 172 world ranking isn’t good enough to get me into overseas events, so getting into The Open by winning this week is amazing. The goal was to be a major player rather than a prize winner.”

He received a cheque for US$178,205.

Campbell closed with a 72 to finish three behind the winner in a tie for eighth and also suffered from a disappointing finish that saw him double bogey 17.

“The Open was my goal at the start of this season ... The goal was to be a major player rather than a prize winner.” - Shugo Imahira.

“Very frustrated with the finish. Lost the ball on 17th. I thought it was on the fairway, but it actually went left,” Campbell said. “It was a week that could have been unfortunately. But overall, still a positive week.

“I thought I was feeling rusty coming into this week and that sort of showed a little bit today. Had a good chance after making birdie on 13 but three putted 14 and that really killed me. I only had about 10 feet there for birdie. To three putt that really hurts.”

Thailand’s Itthipat Buranatanyarat produced one of his best rounds on Tour, a 66, to finish joint 11th.

“I almost couldn’t make it to this event,” said Itthipat, a three-time winner on the Asian Development Tour.

“I had issues with my visa applications because it was quite last minute. I was on the reserve list and only got into the tournament five days before I fly. I am really happy with my result. This is my first Diamond Cup and the first Asian Tour event I’ve played in Japan. I have played in Japan on the Challenge Tour before but never on the Asian Tour.”

Todd Sinnott was the best of the Aussies, the Victorian sharing 18th after closing with a 68.