With barely two minutes on the clock, Korat took the lead when Prompong latched onto a through ball from Yusuke Kato to slot home.
For the rest of the first half, the Division 1 side held the lion's share of the play, yet it was Laem Chabang who came closest to scoring on the stroke of half time with 'Jack' Saranuwat's lob bobbling just wide of the post.
The afternoon heat seemed to sap the energy of both sides as the second half was played at a slower tempo.
The Iron Stingray were slowly getting on top and Ekarat had to spread himself to block Phubet's shot on 70 minutes.
Seven minutes later, the Swatcats were reduced to 10 players after the referee produced a red card for Nirandrit's challenge.
Things went from bad to worse for Korat one minute later when the referee spotted a handball in the box and promptly pointed to the spot.
Prompong then had a low shot smothered as extra time beckoned.
Full time: Laem Chabang 1-1 Nakhon Ratchasima
The hosts had a great chance to score early in extra time, but Prirat skied over the bar after being sent on his way.
Marit headed over for Laem Chabang while Prompong's shot was parried by the home side's keeper as the first period of extra time ended 1-1.
With a penalty shoot out on the horizon, the winning goal was scored in the 111th minute by Shota Koide. The Japanese midfielder curled an exquisite right footer into the top corner giving the Laem Chabang keeper no chance.
That was it as far as the action went. Overall, it was a tough win for Nakhon Ratchasima against a plucky Laem Chabang side.