By ESPNSTAR.com staff
Following a goalless first half in the re-arranged encounter, which was called off on Wednesday due to torrential rain, Chiangrai took the lead in the 46th minute when Uilian Souza scored.
However, Army hit back four minutes after the hour mark through a Tatree Sing-Ha strike, before Australian striker Danny Invincibile proceeded to sent them through to the final when he grabbed what proved to be the winner ten minutes later.
Standing in their path to silverware is Buriram, who saw off Bangkok Glass 2-0 on Wednesday thanks to a Goran Jerkovic brace.
Thursday's Thai FA Cup Semi-final Results
Army United 2-1 Chiangrai United
Wednesday's Thai FA Cup Semi-final Results