Thai League 1 champions Buriram United beat Ratchaburi 2-0 in the League Cup quarter-finals on Sunday night.
Goals from Jonathan Bolingi (48) and Supachok Sarachart (72) sent the Thunder Castle to the semi-finals.
In the last four on May 25, Buriram face Chiang Rai United and Prachuap take on Chonburi.
Prachuap are the defending champions after defeating Buriram in the title match in 2019.
Buriram are five-time champions while Chiang Rai lifted the trophy in 2018.
Sunday's win keeps alive Buriram's hope of sweeping three major domestic competitions.
They are heavy favourites to beat Suphanburi, who were recently relegated from Thai League 1, in the FA Cup semi-finals on May 18.
"We have won the Thai League 1 title but we won't stop here," Buriram chairman Newin Chidchob said in a social media post last week.
"Our goal is to win every tournament in Thailand. We will win the FA Cup and the League Cup for our fans."
Buriram were eliminated in the play-offs of the AFC Champions League this season and Newin vowed the Thunder Castle will try to do better next season.
"We will return to the AFC Champions League next year as Thai League 1 champions," he said.
"We must be better prepared and try to go as far as we can in this tournament."