By Gabriel Tan
Following a goalless first half, it was Harimau Malaya who opened the scoring at the Bukit Jalil National Stadium when Norshahrul Idlan Talaha headed home in the 48th minute after great work down the right by Mahalli Jasuli.
But 11 minutes from time, Teerasil Dangda popped up at the other end and scored with a brilliant header to force a draw, as well as hand his side a vital away goal ahead of next Thursday's return leg in Bangkok.
The result also meant defending champions Malaysia accomplished an unprecedented feat in this year's tournament prior to Sunday - avoid defeat against Winfried Schafer's rampant charges.
The War Elephants certainly headed into their last-four clash in good form after winning all three of their Group A matches, while their opponents bounced back from an opening defeat to Singapore with wins over Laos and Indonesia to seal their progress from Group B.
Although Malaysia's chances of victory ahead of kickoff were dealt a blow when it was revealed star striker Safee Sali was only fit enough to take his place on the bench, it was them who looked the livelier of the two teams in the opening exchanges.
However, it was the visitors that came closest to breaking the deadlock in the 11th minute when Malaysia's failure to clear their lines saw them give the ball away to Adul Lahsoh, whose blistering 25-yard strike was brilliantly tipped wide by Farizal Marlias.
Nine minutes later, it was Thailand's turn to gift K. Rajagobal's side a chance when the backline went to sleep and allowed Azamuddin Akil to sneak in at the far post and meet a searching left-wing cross from Bunyamin Umar. Unfortunately for the Pahang man, the ball took an awkward bounce right at the crucial moment and he was unable to get a clean strike away.
The woodwork then came to the War Elephants' rescue three minutes after the half-hour mark when Teerasil, in an attempt to deal with a Safiq Rahim corner, sent his clearance towards his own goal and looked relieved to see it come back off the post.
A minute later, Safiq threatened with another dead-ball delivery when he lined up a freekick on the left flank and went straight for goal from a tight angle, sending Kawin Thamsatchanan flying to his near post to make the save.
Nonetheless, there was not much the Muangthong United could do to prevent Malaysia from taking the lead three minutes after the break, when Mahalli went on a determined charge down the right before clipping a pinpoint cross onto to head of Norshahrul, who expertly guided the ball into the bottom corner.
While taking the lead was no less than the hosts had deserved given they were arguably the better side in the opening 45, Norshahrul's opener did jolt their opponents into action as they began to show more energy and desire in the attacking third.
Three minutes after the hour mark, Teerasil, who had been having a quiet game up to that point, dealt the Harimau Malaya defence a warning when he outjumped a sea of players to meet a corner from Datsakorn Thonglao, only to send his header just over.
A minute later, the lively Norshahrul nearly helped his side double his lead when he went on a jinking run down the left and skipped inside Chonlatit Jantakam, before drilling in a shot that Kawin could only push back into the danger zone, although none of his team-mates were on hand to pounce on the rebound.
Even though Thailand were beginning to lead in the possession stakes, they were still finding it hard to break down the opposition backline, which was marshalled with authority by Aidil Zafuan.
Instead, Schafer's men were restricted to shots from distance although Farizal was called into making another flying save to keep out a piledriver from Apipoo Suntornpanavej in the 67th minute, before Datsakorn fizzed one just wide from the edge of the area seven minutes later.
Nonetheless, it was always likely that the clinical Teerasil would be the one to find the breakthrough for the Thais, which he eventually did in the 79th minute when he rose majestically to meet a lovely floated ball from Piyaphon Buntao before sending a fantastic header into the top corner from all of 15 yards.
Two minutes later, the visitors' night soured when Schafer, who had spent most of the evening venting his frustrations at the referee down the touchline, was issued his marching orders, meaning he will now miss next Thursday's return encounter.
With their tactician no longer by their side, Thailand looked the more vulnerable side entered its closing stages, and they had Kawin to thank in the 88th minute as he made a fantastic point-blank range save to keep out a bullet header by substitute Safee, after a Zubir Azmi freekick had bounced all the way to the far post.
Malaysia then had one final chance to steal the win four minutes into injury time when Norshahrul somehow found his way in behind the Thai defence, but just as he looked set to test the opposition keeper, Panupong Wongsa slammed the door shut in his face with a terrific recovering block, meaning there will still be plenty to play for at the Suphachalasai Stadium in four days' time.
Malaysia: Farizal Marlias, Mahalli Jasuli, Aidil Zafuan, Fadhli Shas, Bunyamin Umar (Zubir Azmi 86'), Amar Rohidan (Safee Sali 75'), Gary Robbat, Azamuddin Akil, Safiq Rahim, Baddrol Bakhtiar (S. Kunanlan 75'), Norshahrul Idlan Talaha.
Thailand: Kawin Thamsatchanan, Piyaphon Buntao, Panupong Wongsa, Chonlatit Jantakam, Theerathon Bunmathan (Sompong Soleb 52'), Adul Lahsoh (Apipoo Suntornpanavej 59'), Pichitpong Choeichiu, Datsakorn Thonglao (Kirati Keowsumbat 76'), Jakkapan Pornsai, Anucha Kitpongsri, Teerasil Dangda.