By ESPNSTAR.com staff
Montenegrin midfielder Dordije Cetkovic opened the scoring for Buriram after 12 minutes when he pounced on a rebound to tap in at the far post, before Goran Jerkovic doubled their lead ten minutes with a close-range header.
Jerkovic then added another in the 25th minute when he raced through and coolly slotted home, and three minutes after the half-hour mark, Cetkovic made it 4-0 with another easy finish after Ekkachai Sumrei's deft chip had come back off the crossbar.
Ratchaburi pulled one back on the stroke of halftime when they were awarded a penalty, but Buriram picked up where they left off after the break and scored three more, including a third for Jerkovic, to cap off an excellent night at the office.
Next up for Attaphol Puspakom's charges is BEC Tero Sasana, who recorded a 3-1 win over fellow Premier League side Samut Songkhram.
Muangthong United booked their place in the last eight after beating Nakhon Ratchasima 2-0 at the SCG Stadium.
Following a goalless first half, Bolivian striker Edivaldo Hermoza broke the deadlock in the 68th minute, before Paulo Rangel wrapped things up in injury-time with a second following a neat pass from Mario Gjurovski.
The Twin Qilins' quarter-final opponents will by Army United, who beat PTT Rayong 3-1 on penalties following a 0-0 draw at the PTT Stadium.
Hironori Saruta scored the only goal of the game in the 83rd minute to hand Bangkok Glass a 1-0 win over Chainat, setting up a clash with Ayutthaya, who came from a goal down to record a stunning 2-1 triumph over top-flight side Thai Port.
Finally, Chiangrai United beat struggling Police United 5-4 on penalties after a 2-2 draw and will next meet Suphanburi, who defeated fellow Division 1 side Songkhla 1-0.
Wednesday's Thai FA Cup Fourth Round Results
Muangthong United 2-0 Nakhon Ratchasima
PTT Rayong 0-0 Army United (1-3 on pen.)
Chiangrai United 2-2 Police United (5-4 on pen.)
Songkhla 0-1 Suphanburi
Buriram United 7-1 Ratchaburi
BEC Tero Sasana 3-1 Samut Songkhram
Bangkok Glass 1-0 Chainat
Ayutthaya 2-1 Thai Port