By ESPNSTAR.com staff
The reigning champions took the lead at the Thunder Castle Stadium in the 47th minute through Yves Ekwalla Herman, before French striker Goran Jerkovic doubled their lead two minutes later.
20 minutes from time, Adisak Kraison grabbed a third for Attaphol Puspakom's side to cap off an excellent night at the office and end BEC Tero's hopes of going all the way in the competition.
Thai Premier League leaders Muangthong United conceded twice in the final ten minutes to allow Army United to record a shock 3-2 victory at the Thai Army Sports Stadium.
Nipol Kamthong had fired the hosts ahead in the 32nd minute but after Teerasil Dangda had equalised on the stroke of halftime, Paulo Rangel grabbed a second and it looked as though Muangthong were on their way to a routine win.
However, German midfielder Bjorn Lindemann equalised for Army in the 80th minute and six minutes later, captain Tatree Sing-Ha netted to hand the hosts a spot in the last four.
Standing in the way of Army and a place in the final will be Chiangrai United, who needed extra-time to see off the challenge of Division 1 side Suphanburi with a 3-1 triumph at the United Stadium.
Brazilian forward Leandro Assumpcao put the Fighting Beetles in front two minutes after the half-hour mark, only for Worrawoot Srimaka's to hit back in the 73rd minute thanks to a Nawin Channgam strike.
And with neither side able to find a second in the remaining 17 minutes, the game then proceeded to extra-time, where Chiangrai eventually prevailed thanks to goals from Wasan Natasan and Nantawat Tansopa.
Completing the line-up in the semis will be Bangkok Glass, who survived a late scare to beat Ayutthaya 2-1.
Anawin Jujeen opened the scoring for the Glass Rabbits in the 37th minute, before Thailand international Teeratep Winothai made 2-0 in first-half injury-time.
Ayutthaya did pull one back at the death but it was a case of too little too late for the Ancient Warriors, who can still be proud they made it all the way to the quarter-finals.
Wednesday's Thai FA Cup Quarter-final Results
Ayutthaya 1-2 Bangkok Glass
Army United 3-2 Muangthong United
Buriram United 3-0 BEC Tero Sasana
Chiangrai United 3-1 Suphanburi (after extra-time)