AGMK pressured the Vietnam club from the start with quick counter-attacking play which would have yielded goals if not for the alertness of Thai Son Nam custodian Ho Van Y.
Davron Choriev, Akbar Usmonov and Anaskhon Rakhmatov were a thorn in Thai Son Nam’s side as the trio controlled play in their attacking half.
AGMK, who reached the quarter-finals in 2016, came close to scoring in the sixth minute when Rakhmatov unleashed a long-range effort from above the box but his effort was easily saved by Ho.
The Uzbekistan club kept up the tempo and were rewarded seconds later when Usmonov scored the opening goal after being fed by Choriev.
Thai Son Nam, who finished runners-up in 2018, certainly took their time to mount attacks as they toiled in front of the AGMK goalmouth in search of the equaliser.
In the 11th minute, Pham Minh Giang’s side finally showed their attacking prowess when Nguyen Minh Tri scored a beautiful left-footed volley from 15 metres out to level the score.
Both teams battled hard to break the deadlock with Thai Son Nam coming closest in the 17th minute when Kazuya Shimizu broke free from his marker but his effort fell straight into the arms of AGMK custodian Rustam Umarov.
Thai Son Nam started the second half with purpose and AGMK’s defence gave way when Ton That Phi scored in the 22nd minute to give the Vietnam club a 2-1 lead.
AGMK refused to give in and picked up the pace as they battled hard to level the score.
Khusniddin Nishonov came close to scoring in the 29th minute when he lost his marker at the top of the box but with only the goalkeeper to beat, sent his effort high above the bar.
Thai Son Nam were quick to respond and in a swift move, Tran Thai Huy rounded Umarov at the top of the arc and finished clinically.
Tran Thai Huy doubled his tally four minutes later when he latched on to Alireza Rafiei Pour’s pass to slot home Thai Son Nam’s fourth goal from close range to seal a dream start for Thai Son Nam.