The big-hitting 23-year-old held his nerve for a battling two-under-par 70 to lift his second Asian Tour title by one-shot from Ryder Cup star Edoardo Molinari of Italy, who signed off with a 67, at the Kuala Lumpur Golf and Country Club.
Anders Hansen of Denmark shot a 66 to finish two shots back while 2011 Masters champion Charl Schwartzel of South Africa settled for tied fourth position following a 71 in the US$2.75 million championship sanctioned by the Asian Tour and European Tour.
Kiradech, who is the fourth Thai after Thongchai Jaidee, Thaworn Wiratchant and Chapchai Nirat to win a co-sanctioned tournament, said: "I'm so happy this week. I'm proud of myself and for my family. I almost won here a few years ago (2010) and finally I made it. I'm so happy.
With a winner's cheque of US$458,330, Kiradech jumped to the top of the Asian Tour's Order of Merit with his season's haul of US$594,230.
The burly Thai, dubbed Asia's John Daly due to his physique and style of play, had to overcome tiredness because of a thyroid problem and four days of weather disruptions to prevail at the Maybank Malaysian Open which was reduced into a three-round tournament.
He led by one shot through 15 holes of the third and final round when play was suspended for two hours because of a lightning storm and came back out shaking at the prospects of winning his career's biggest title yet.
He birdied the 16th hole upon the resumption of play from four feet to open up a two-shot advantage and then enjoyed a stroke of fortune when his approach into the 17th green ended just a few feet from the water hazard. After leaving his chip some 15 feet short of the flag, Kiradech drained his par putt and celebrated with a clenched fist.
Playing it safe with an iron off the tee on the last, a closing bogey did not matter as his three-day total of 13-under-par 203 was one clear of Molinari.
"After I made birdie on 16, I knew I had a chance to win. But in golf, you can't say you can win when you're not finished. I was lucky my ball was still safe (on 17). If it rolled into the hazard, it would be tough to win. But I concentrated hard on 18. I've played here for about 20 times, and on 18, I think I've birdied it more than 10 times. Bogey was so tough but it was good enough to win," said a beaming Kiradech
"During the suspension, I couldn't eat anything. I was so excited. When I walked out, everything was shaking, even my voice. My caddie told me to just concentrate, just two more holes. I'm lucky that I played only 54 holes. Otherwise, I am so tired due to the weather and the golf course."
Molinari, who was getting ready to warm up for a possible play-off, was disappointed he only made par at the closing 18th hole after a wayward drive. "I felt if I birdied the last I might have won outright because it puts a lot of pressure on the guy coming up behind," said the Italian.
"It's mixed emotions because I'm very happy to have a good week for the first time in a long time. The swing changes (with new coach Sean Foley) are starting to pay off which is surprising because I thought it would take a lot longer. But I'm disappointed because I had a lot of chances on the back nine. The 18th is only the second fairway I missed all day which is very disappointing."
Schwartzel, playing in the last group with Kiradech, rued the missed opportunity to emulate countryman Louis Oosthuizen, who won the Maybank Malaysian Open last season. "It was disappointing. It's a hard week with being on and off the course the whole time. It's difficult to find any rhythm. I feel like I swung the club pretty well, but I didn't play that well today," said the South African, who was searching for his second title in Asia after winning the Thailand Golf Championship last December.
"I was hitting terrible iron shots from the middle of the fairways. That's my strength. For some reason I was hitting short irons all over the shop. What can I do? Kiradech did well. I would've liked to have applied a bit more pressure on him."
China's Wu Ashun was the next best Asian in tied 11th place on 208 after closing with a 73 while Malaysian amateur Gavin Green enjoyed a creditable equal 22nd place finish after a closing 69 fir a 210 total.