Thai veteran Thaworn Wiratchant dropped four shots over his last five holes in a rare lapse that allowed three rivals into a share of the third-round lead in the Queen's Cup in Koh Samui on Saturday.
Thaworn was four shots ahead on another blustery day at Santiburi Samui Country Club before his game unravelled with some misjudged tee-shots for a one-over-par 72 and three-day total of four-under-par 209.
Unheralded Thai Varut Chomchalam, 23, produced a superb 66 to charge into the joint lead after starting the day six back while Bangladeshi Siddikur rammed in a seven-foot birdie putt at the closing hole for a 71.
Philippine teenager Miguel Tabuena, who has held a share of the lead since day one, overcame a double bogey and two bogeys with three birdies to ensure he has a chance of becoming the fourth youngest winner on the Asian Tour.
At the end, Thaworn, who is chasing a record-equalising 13th Tour victory, was kicking himself for losing his grip on the $300,000 Queen's Cup, the 11th leg of this season's Asian Tour.
"I only have myself to blame," said the 45-year-old, who won at Santiburi Samui in 2008 and was runner-up two years ago.
"I didn't play well on the last three holes, couldn't tee off well and when you get into bushes or jungle, it is not good."
The surprise of the day came from Varut, who has never posted a top-10 on the Asian Tour. He stole the thunder with a seven-birdie round against a double bogey to put himself in position for glory.
"Everything was perfect. The past few years, I learned about the game by playing on the Asian Tour," he said.
Leading scores after round three of the Queen's Cup Bangkok Airways:
209 - Varut Chomchalam (THA) 72-71-66, Siddikur (BAN) 70-68-71, Thaworn Wiratchant (THA) 70-67-72, Miguel Tabuena (PHI) 67-70-72
211 - Panuwat Muenlek (THA) 71-73-67, Jonathan Moore (USA) 72-72-67, Guido Van Der Valk (NED) 70-72-69, Baek Seuk-Hyun (KOR) 68-73-70, Anirban Lahiri (IND) 71-68-72
212 - Juvic Pagunsan (PHI) 75-65-72© ANP/AFP