Poomjaeng, who regained professional status in August following a five-year absence, was on course for a major upset after scraping the second frame in Brentwood on a respotted black.
The Thai player kept the crowd entertained with some captivating antics around the table but ultimately fell short of masterminding a shock in a 4-2 loss.
Seven-time world champion O'Sullivan, who battled back to set up a meeting with Martin Gould, admitted he was amused by his rival's behaviour, likening him to Rowan Atkinson's famous comedy creation.
"I thought there was no point just trying to play straightforward snooker, let's just have a laugh," O'Sullivan, who made a break of 104 in the penultimate frame, told wst.tv.
"I went for some doubles and trebles, some of them went in, crazy things can happen when you go for it.
"He's like a Mr Bean type character, he pulls these funny faces and his mannerisms - he should go into comedy, he'd be a great character.
"I was enjoying just going for my shots and trying to make something happen."