The Crucible crowd witnessed a thrilling and incident-packed match, gradually warming to the previously unheralded 34-year-old from Saraburi as he registered one of the biggest shocks in recent years at Sheffield.
From going to the wrong table when he was introduced into the arena, to knocking over a bottle of water with his backside, to his animated nature around the table, Poomjaeng provided plenty of entertainment. The only person who wasn't laughing was Maguire, but even the Scot produced a wry smile as his opponent - ranked 65 places below him at 70th in the world - compiled an excellent break in the deciding frame.
Poomjaeng, who had to win four qualifying matches to reach the Crucible for the first time, goes through to the last 16 to face fellow debutant Michael White, while Maguire must wait 12 months for another crack at fulfilling his biggest goal of winning snooker's most prized title.
After trailing 5-3 overnight, Maguire looked in much better shape today after winning the first three frames with breaks of 70, 91 and 93. But Poomjaeng hit back with a 74 clearance in the next then dominated frame 13 to lead 7-6.
The next four were shared to leave the score at 9-8 when the second session was brought to a premature end. On the resumption tonight, Maguire built a 46-11 lead in frame 18, then Poomjaeng had a chance to clear but missed a tricky final brown with the rest on 34. Maguire also missed it, but then won a safety battle and cleared to the pink to force the first decider of the tournament.
Handed a chance early in the last frame, Poomjaeng made an excellent 63 before running out of position. Maguire had one more chance but missed a tough red to a centre pocket and his opponent sealed the result with a run which ended on 41 when he missed the last blue with his eyes closed.
"It's a big surprise because Maguire is a top-five player and I thought I only had a 10 or 20 percent chance of beating him," said Poomjaeng, who won the world amateur title in 2010 and has been on the pro tour for two seasons. "In the last frame I just tried to play and take it one shot at a time.
"I believed in myself. I knew it would be very hard but I hoped I could win if I got chances. I tried to just relax and enjoy it because I knew if I was too serious it wouldn't be good for my game. It was exciting at the start because there were lots of people and it was my first time at the Crucible.
"I hope I play well in my next game, but win or lose I'll be happy. I'm happy that people like me. I enjoy the game and hope people enjoy it with me."
Maguire joked: "I don't think he's the full shilling. I've never seen him before but there's definitely something missing. He seems like a really nice boy and very genuine. The crowd seemed to take to him and got behind him at the end and he seemed to be enjoying it.
"I was afraid to look at him in the end. Crazy things were happening out there. I just had to switch off. All I can say is that he's a nice lad.
"It just wasn't meant to be for me. Take nothing away from him, he made some great breaks all through the match and luck favours the man who plays well and he played better than me.
"It's disappointing for me but I could tell the way the match was going. I had a bad feeling about it."
He beat John Higgins in his first professional match, at PTC1 in 2011.
He reached the last 32 of the German Masters and China Open earlier this season and is now through to the last 16 of a ranking event for the first time.
He is based in Sheffield during the season, practising at the Star Academy with the likes of Ding Junhui.
He shares a house with four other Thai players, including former world number three James Wattana, who he describes as "like a brother."
His nickname among his fellow players is Jack.
His older brother is Suchakree (better known as Kwan) Poomjaeng who has also played on the professional tour.
Ball by ball scoring and results from tournaments