Porthmadog up to third.
CRAIG ROBERTS'' goal early in the second half proved enough to secure the win which moved Porthmadog up to third in the Huws Gray Alliance and ended a run of three successive defeats.
Although the Traeth outfit started strongly they found a defence-minded Guilsfield difficult to break down and the visitors almost grabbed a shock lead when Nathan Leonard crashed a shot against the bar.
It was Port, however, who deservedly went ahead on 27 minutes when Mark Jones broke to the byeline and crossed for Darren Thomas to score.
The game was becoming physical and on the half-hour a terrible tackle on Thomas led to a flare-up involving several players.
The referee responded by showing Guilsfield''s Rob Cookson a red card for the challenge and also gave Port''s Mark Jones his marching orders for retaliation.
Gareth Jones Evans tested Guils keeper Dave Littleford with a lob, but the mid-Walians were now a bit more adventurous on the counter and from one such break Ian Probert lifted the ball over keeper Richard Harvey to make it 1-1 at half time.
Five minutes into the second stanza Port restored their lead with the best move of the match.
Good work by Thomas led to Chris Williams floating over the perfect near-post cross for Roberts to head past Littleford.
After that Port pressed for a third but found Littleford reluctant to be beaten again as he produced good stops from Jones Evans, Thomas and Iwan Williams.
Guilsfield remained a threat on the break and Harvey did well to foil Probert and Leonard.
With eight minutes of added time, Guils threw everything into attack, but Port held on for a welcome three points.