By FOX Sports staff
In extremely wet conditions at the New I-Mobile Stadium on Wednesday, it initially looked as though the Thunder Castle were going to be denied as they struggled to find the back of the net despite carving out a plethora of chances throughout the 90 minutes.
But in the sixth minute of injury time, a freekick from Jirawat Makarom could only be cleared straight into the path of Charyl Chappuis, who clinically lashed home the rebound into the bottom corner to hand Buriram the slimmest of leads heading into the second leg.
Army United were also victors on the night as they claimed a hard-fought 1-0 victory over Nakhon Ratchasima.
Following a goalless first half at the Thai Army Sports Stadium, the deadlock was broken in the 72nd minute when Jung Myung-oh reacted quickest after opposition goalkeeper Munze Ulrich had parried a blistering freekick by Bjorn Lindemann, and netted what proved to be the winner.
Chonburi fell to a shock 1-0 loss to fellow Premier League outfit Ratchaburi at the Ratchaburi Stadium; Saenee Kaew-nam scoring the only goal of the game a minute before the break with a well-taken finish.
Finally, Rayong FC struck late to salvage a 1-1 draw at home to Looktabfah in Wednesday's final quarter-final clash.
It initially looked as though the visitors were going to claim a vital away win as they were leading through Rachan Ganjina's 22nd-minute effort, but seven minutes from time, Abdel Azizou Takeu struck to keep the Wild Horses in the tie.
Wednesday's Thai League Cup Quarter-final First Leg Results
Ratchaburi 1-0 Chonburi
Rayong FC 1-1 Looktabfah
Buriram United 1-0 Udon Thani
Army United 1-0 Nakhon Ratchasima
Image courtesy of Buriram United FC