The popular duo were tied for 12th, five shots off the pace set by Robert Allenby of Australia at The Mines Resort and Golf Club.
Indian stalwart Jeev Milkha Singh, a two-time Order of Merit winner, was a further shot back in tied 19th place in the Asian Tour and PGA Tour-sanctioned event.
Siddikur was four-under going into the last hole before an errant approach shot landed in the green-side rough which forced him to settle for a bogey.
Thongchai, playing for the fifth consecutive week, struggled with fatigue but managed to return with five birdies against two bogeys at The Mines Resort.
“My body is a bit tired. I had a good sleep in the last two days. I’ll try to get good rest today and get myself ready,” said the three-time Asian Tour Order of Merit winner, who has a game plan for the uncut format.
“You have to attack the pin all the time. There’s nothing to lose. I want to aim for low scores. Longest iron in is no more than a seven or six iron. But you need some luck as well,’’ said Thongchai, two shots ahead of countrymen Chinnarat Phadungsil and Kiradech Aphibarnrat, who both scored 70.
Today, ThaiBev led by executive director Surapol Utintu will take 20 Thai amateurs from the Chang Golf Day and three juniors from the Chang PGA Academy Golf Clinic to witness the weekend rounds.
King’s Cup postponed
The King’s Cup golf tournament, originally scheduled for December 8-11 at the Singha Park Khon Kaen Golf Club, has been postponed in deference to the critical flood situation and efforts to help victims in the local community.