Dunfermline Athletic 1 Hibernian 0
The Pars were struggling to cope with the trickery of Abdessalam Benjelloun early in the match with the Moroccan creating a great chance for himself as Dorus De Vries saved easily.
Then the striker's wing play set up Guillaume Buezelin for a simple effort but the Frenchman sliced his shot wide.
The Pars marched straight up the park and almost took the lead on the counter attack. Veteran Jim McIntyre found himself clean through on goal but Andrew McNeil spread himself well to foil the striker.
The resultant rebound fell to the feet of Tam McManus but the striker could only shoot tamely into the sidenetting.
McManus tested McNeil's reflexes minutes before half-time, as the former Hibs player rifled in a swerving free kick that the keeper did well to tip over the bar.
Dunfermline were matching Hibs for attacking endeavour and could have taken the lead on the hour mark. Souleymane Bamba won the ball at a corner and the defender's knock down fell into the path of McIntyre.
The striker's overhead kick appeared to be net-bound, only for McNeil to produce a stunning one-handed save to deny the Pars.
McManus was next in line to try his luck with a spin and shot from 20 yards that flashed just wide of the upright.
It was the Pars who ultimately took all three points from the unlikeliest of heroes in McGuire. The centre-half ambled forward to meet an Adam Hammill free-kick, powering his header into the net from eight yards out, to give the home side a crucial lead.
Hibs pushed forward in an attempt to salvage something from the match and were caught on the break as Rob Jones went to ground, allowing substitute Mark Burchill a clear route on goal.
The former Celtic striker could only watch in anguish as McNeil managed to get a hand on Burchill's shot to divert it wide of the post.
The Pars will display great interest in St Mirren's clash with Rangers tomorrow, in the hope the Gers can serve up a huge favour to the East End Park club in their battle to avoid the drop, with the Buddies now only four points ahead in the league.