The Thai fighter had previously defeated Chilson at One FC: Pride of a Nation but the referee had deemed a soccer kick within that contest to have been an illegal move.
Subsequently, the One FC rules had been changed and a rematch had been organised between the duo at the Singapore Indoor Stadium on Friday night.
Wiratchai appeared eager to settle the score but was quickly on the defensive when Chilson took his opponent to the edge of the cage in a bid to carry out an early takedown.
The BurnShell Team fighter did not allow the American to get a firm hold of him, though, and even avoided a reverse elbow before landing a powerful left hook that floored Chilson.
Chilson lost his balance and was at the mercy of Wiratchai who pummeled the 35-year-old's head with two swift kicks and pounced on his opponent to finish the job, only for the referee to come to the Evolve fighter's rescue and call a premature end to the three-round contest.
With the win, Wiratchai became the first fighter to defeat a member of Team Evolve this year, with the Singapore gym having previously racked up nine wins across four tournaments in Kuala Lumpur, Singapore, Manila and Manila.
Aside from the grudge match, the local crowd also had reason to cheer as the Singaporean trio of Sherilyn Lim, Juan Wen Jie and Stephen Langdown defeated fighters from across the Causeway in Ann Osman, Alex Lim and Marc Marcellinus respectively.
Khim Dima also became the first fighter from Cambodia to achieve a win at One FC when he secured his victory via referee stoppage against Philippines' Rene Catalan.