By Gabriel Tan at the Rajamangala Stadium
The War Elephants edged ahead in the 20th minute through an ingenious strike from Teerasil Dangda, before substitute Apipoo Suntornpanavej doubled their lead on the hour mark when he powered home a header shortly after coming on.
Eight minutes from time, Teerasil added his second after a glorious pass from Theerathon Bunmathan, before completing his hat-trick seven minutes later to seal an emphatic rout for the hosts.
While the result was enough to send the Thais through to the last four ahead of their final group encounter against Vietnam, Myanmar will now need to beat Philippines on Friday to have any chance of progressing from the group.
Having seen his side open their campaign with an impressive 2-1 victory over the Azkals on Saturday, Thailand coach Winfried Schafer opted to stick with a winning formula by naming the same starting XI, with the exception of influential midfielder Datsakorn Thonglao, who missed out with a thigh injury.
In his place came Sumanya Purisay, although it was Pichitpong Choeichiu who took as their playmaker-in-chief, and five minutes in, he nearly opened the scoring when he was left in acres of space on the edge of the box and unleashed a shot that sailed narrowly over the bar.
12 minutes later, Pichitpong showed why he was handed the job as he carved open the opposition defence with a delightful ball to pick out Jakkapan Pornsai, but the winger's control let him down and he could only watch as the ball rolled safely into Thiha Sithu's gloves.
Despite the hosts' dominant start, Myanmar were looking rather dangerous on the counterattack, and they had a good chance to score with their first real foray forward in the 18th minute; Kyi Lin playing a neat through-pass to pick out the unmarked David Htan inside the area, only for the Yangon United man to screw his shot wide.
That miss proved costly for the White Angels just two minutes later as Thailand found the breakthrough, after Pichitpong lofted another visionary pass over the top to Teerasil, who brillianty brought the ball past his marker with his first touch, before clinically firing into the back of the net.
Four minutes after the half-hour mark, Sumanya nearly made it 2-0 when he picked up possession 25 yards out and hammered an effort towards goal but Thiha Sithu managed to push it wide, albeit in unconvincing fashion.
The Myanmar goalkeeper did however do well in the 42nd minute when he raced off his line and punched away a dangerous cross by Theerathon Bunmathan, especially given the ever-dangerous Teerasil was lurking nearby.
Theerathon, who was bombing down the left flank at every possible opportunity, then whipped in another tantalising delivery into the box and this time, there was nothing Thiha Sithu could do but watch on in relief as Jakkapan's near-post header flew just wide.
Seconds later, the War Elephants had another chance when Sumanya sent Teerasil through on goal with a lovely dinked pass, but the Muangthong United star tried to be slightly too clever and got his attempted lob over the onrushing keeper woefully wrong.
Nonetheless, there was no denying Thailand right on the hour mark when Anucha found space down the left and floated a terrific cross onto the head of Apipoo, who - only two minutes after coming on - proceeded to power a header that crept into the back of the net despite Thiha Sithu's best efforts.
Ten minutes later, the Osotspa Saraburi man nearly doubled his tally when his firm effort was just kept out at the near post, after he had raced down the right and cut inside on his left foot.
By now, Myanmar were starting to look increasingly deflated but they could have pulled one back in the 78th minute when substitute Aung Moe fired a curling freekick towards goal that Kawin Thamsatchanan commandingly caught with a diving save.
However, that effort was one of the few things of note that Myanmar conjured up all evening long and four minutes later, the contest was effectively ended then Thailand grabbed their third, Teerasil latching onto a lovely over-the-top pass by Theerathon and racing towards goal before coolly slotting into the bottom corner.
Although their place in the last four was now already in the bag, Schafer's charges showed no signs of letting up and Teerasil capped off a fine night at the office a minute from time when he raced through to meet a glorious pass by Sompong Soleb and fired home to complete his hat-trick.
Myanmar: Thiha Sithu, Zaw Zaw Oo (Thet Naing 69'), Aung Hein Kyaw, Zaw Min Tun, Pyaye Phyo Aung, Yan Aung Kyaw, Naing Lin Oo (Aung Moe 73'), Khin Maung Lwin, David Htan, Kyi Lin, Yan Paing (Kaung Sithu 68').
Thailand: Kawin Thamsatchanan, Piyaphon Buntao, Panupong Wongsa, Chonlatit Jantakam, Theerathon Bunmathan (Sompong Soleb 82'), Adul Lahsoh, Sumanya Purisay (Apipoo Suntornpanavej 58'), Jakkapan Pornsai, Pichitpong Choeichiu (Arthit Sunthornphit 71'), Anucha Kitpongsri, Teerasil Dangda.
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