American Chan Kim narrowly missed out final-hole birdie to force a playoff as Hideto Tanihara surprised himself by overturning a four-shot deficit to end his 12-month winless run on JGTO with a successful defence of his Golf Nippon Series JT Cup on Sunday.
Tanihara, 44, carded five birdies to close with a five-under-par 65 at the Tokyo Yomiuri Country Club for a winning total of 12-under-par 268 which was good enough for him to hold off Kim, Hiroshi Iwata and Daijiro Izumida for a one-shot victory.
Kim, the 2020 winner, birdied the 17th hole to get within a shot of Tanihara and was standing over the fifth birdie putt from about eight feet on the challenging par-three 18th with a chance to tie.
However, the 32-year-old failed to convert the clutch putt and settled for a nevertheless impressive bogey-free 65 to finish runner-up for the second time this season.
"It's the famous 18th green right? It's a very, very tough putt," said Kim, who fell just short of making it a back-to-back victory following last week's triumph at the Casio World Open.
"Basically, you have to aim 90 degrees from the hole but I think I did pretty well to actually make a par there.
"I knew I had to give it a chance there and got a little bit too aggressive with the putt.
"All in all, I played really great. A five-under on this course is a really good round and I'm happy with how I finished."
Despite the season finale disappointment, Kim would still be delighted to finish the season so strongly.
With just 12 appearances this year, Kim, the Money Ranking winner of the 2020-21 season, emerged as the best-placed international member yet again, this time in seventh place after accumulating ¥86,805,149.
Kim is now looking forward to enjoying the off-season where he will marry his sweetheart Sung Lim 'Sally' Choi in South Korea next weekend before heading to Maldives for their honeymoon.
Tanihara was left pinching himself after coming from four shots back to become the first player to retain the title since Hiroyuki Fujita accomplished the feat in 2012.
"I didn't expect to win, so I'm really happy," said Tanihara after clinching his 17th Tour title.
"I waited, thinking that there was nothing to be done even if it was a playoff.
"My golf is not bad, so I thought I had a chance at today's green speed. I'm happy to win the last game of the season."
Third round leader Satoshi Kodaira blew a two-shot cushion as he could only manage a 71 to tie for fifth with two-time winner Ryo Ishikawa (65) on 10-under.
Australia's Brad Kennedy also shot his worst score of the week, a 71, to slip six rungs to tied eighth on 272.
Another two internationals in the 30-man field this week, Anthony Quayle and American Todd Baek shot 66 and 71 to be tied for 18th and 27th respectively.
Leading final round scores:
(Japan unless stated)
268 - Hideto Tanihara 66-67-70-65;
269 - Hiroshi Iwata 68-66-70-65, Chan Kim (US) 65-72-67-65, Daijiro Izumida 66-70-65-68;
270 - Ryo Ishikawa 68-68-69-65, Satoshi Kodaira 66-66-67-71;
271 - Rikuya Hoshino 67-69-67-68;
272 - Yuto Katsuragawa 67-69-70-66, Taiga Semikawa 70-67-69-66, Yuki Inamori 65-69-70-68, Brad Kennedy (Aus) 66-66-69-71.