Like the improvisational music genre with which he shares a name, Jazz Janewattananond marched to his own tune yesterday at the US$1 million (S$1.36 million) SMBC Singapore Open, and no one could keep up with his rhythm.

Despite former world No. 3 Paul Casey snapping at his heels, the Thai struck all the right chords to fire a six-under 65 in the final round and claim the biggest win of his fledgling career.

His winning total of 18-under 266 (68-68-65-65) was two shots better than Casey (68-67-68-65) and Japan's Yoshinori Fujimoto (67-67-66-68).

It was the lowest winning score at Sentosa Golf Club's Serapong Course, surpassing the 17-under 267 set by three-time Singapore Open winner Adam Scott in 2010.

After coming up short in his previous Singapore Open outings - third, second and fifth - he tried a different tack to deal with the pressure, and it worked wonders.

"You know, when I was sitting here previously doing the pre-tournament interviews, I wasn't planning on winning.

"My goal was just to grab one of the four qualifying spots for The Open Championship," said Jazz, who picked up the winner's cheque of US$180,000 (S$244,500).

"I was still thinking the same thing this morning. It wasn't until the back nine that I felt, 'Oh, I could actually win this', and then the pressure was on."

Jazz, 23, was in cruise control after five birdies on his front nine gave him a three-stroke lead.

But the birdies dried up on the back nine and victory looked to be slipping from his grasp after a bogey on the par-4 13th saw his lead over Englishmen Casey and Matthew Fitzpatrick cut to one.

The Thai then displayed nerves of steel to make a par save on the 15th and sink a clutch birdie on the 16th.

Building on his momentum, the world No. 111 conjured up a superb second shot on the par-five 18th that landed about five feet from the pin. He missed his eagle putt when the ball spun out, but he made no mistake with his birdie chance to end the hopes of Casey and flightmates Fitzpatrick and Fujimoto. Fitzpatrick (68-67-66-69) finished alone in fourth on 270 after consecutive bogeys on the 15th and 16th.

Jazz credited his coach Peter Cowen, whom he started working with after his Major debut at last year's Open Championship, for helping him improve his ball striking and mental strength.

"In the past, I didn't really know what I was doing. I was pretty much just going out there and playing. But (working with Pete) has given me goals, things I want to do on the golf course," said Jazz, who became the youngest golfer at 14 years and 71 days to make the cut on the Asian Tour at the Asian Tour International in 2010.

"When you go out to play without thinking of anything, sometimes it can be good but, under pressure, it's tough (to have no goals). That was my mistake in the past."

Jazz is the third Thai to win the Singapore Open, after Prayad Marksaeng in 2017 and Thaworn Wiratchant in 2001.

Defending champion Sergio Garcia of Spain finished joint seventh on 276 (69-68-71-68). Johnson Poh (71-70-69-72) was the top local finisher, tying for 38th on 272.

He said: "This is my eighth time playing the Singapore Open and the first time I made the cut, so overall, it was a great week."

Jazz's third Asian Tour win will see him in the top 100 of the world rankings for the first time. It also earned him a second trip to The Open Championship in July.

He will be joined by Fujimoto, compatriot Prom Meesawat and South Korean Mun Do-yeob, who clinched spots by virtue of being the top four finishers not otherwise exempt.

Asked if he thinks he can be the first Thai to win a Major, Jazz said: "When I was younger, everyone said I would be the first Thai guy to win on the PGA Tour, the first Thai guy to win a Major.

"But, in reality, (world No. 37) Kiradech (Aphibarnrat) is the one with the biggest chance. He's my role model. My next goal is to try and get more wins on the Asian Tour and then see what happens."