By ESPNSTAR.com staff
Kirati Keawsombut opened the scoring for the War Elephants in the 21st minute, before adding a second five minutes after the hour mark.
Although Vietnam hit back in in the 72nd minute through Nguyen Van Quyet, Nguyen Gia Tu scored an own goal eight minutes to send his team crashing out of the competition.
The result highlighted Thailand's strength in depth, given coach Winfried Schafer, having already secured their passage to the last four, opted to rest several of his key players, including star striker Teerasil Dangda and rising left-back Theerathon Bunmathan.
Their weakened side did look vulnerable early on and the Red Stars were unlucky not not to open the scoring in the sixth minute when Cao Sy Coung sent a shot back off the crossbar.
However, the hosts gradually found their groove and threatened the opposition defence for the first time in the 19th minute when Apipoo Suntornpanavej whipped in a good cross that Nguyen Minh Duc was alert enough to clear away.
Nonetheless, Thailand hit the lead a minute later when Apipoo once again caused havoc by darting into the visitors' box, before laying it off to Kirati for an easy finish.
Knowing anything less than a win would end their semi-final prospects, regardless of the outcome of the other game between Philippines and Myanmar, Vietnam started to show more drive and Kawin Thamsatchanan produced a smart stop to push away an effort from Nguyen Trong Hoang in the 39th minute.
Still, what seemed a difficult task was made near impossible five minutes after the hour mark when Kirati netted his second with a firm header, after Sumanya Purisay had ghosted past his maker and sent in a beautiful cross into the box.
Vietnam were handed a boost 18 minutes from time when Arthit Sunthornpit was issued his marching orders after lashing out at Pham Thanh Luong, and they made immediate use of their numerical advantage by pulling one back a minute later when Van Quyet met a Sy Cuong cross with a ferocious shot into the back of the net.
However, it was not to be for the Red Warriors as they handed Thailand a third ten minutes later when Gia Tu turned the ball into his own net, compounding a miserable day at the office.