Lincoln's Richard Butcher scored the only goal of a keenly contested match as opponents Bournemouth still made it through to the play-offs despite their first home defeat for seven months.
Butcher scored with Lincoln's only shot on target, a 26th minute right foot effort which gave goalkeeper Neil Moss no chance.
Lincoln had the better of the first half but came under severe pressure after the break and held on to give themselves a great chance of joining Bournemouth in the play-offs.
Bournemouth, who last lost at home in September, twice hit the woodwork and found goalkeeper Alan Marriott in commanding form.
Marcus Browning struck the inside of the post in the 48th minute with a low right foot shot which rebounded into the arms of the grounded goalkeeper.
After 62 minutes winger Danny Thomas hit a post with an intended centre as Lincoln held on precariously.
Marriott also made an important stop from another close range shot from Browning but Lincoln showed why they have the meanest defence in the Third Division.
The Cherries sent on talisman striker Steve Fletcher for the last 30 minutes despite nursing a shoulder injury which should have ruled him out.
But the powerful Fletcher was well watched by a Lincoln defence in which Paul Morgan and Ben Futcher were outstanding.
All this was in contrast to the first half in which Lincoln were on top long before Butcher's goal.
Paul Smith saw his deep centre tipped over at full stretch by Neil Moss before Bournemouth began to get a grip.
Derek Holmes and Carl Fletcher both headed over from good positions as Bournemouth went in search of an equaliser.
Lincoln's surprise win leaves them needing only a point from their final fixture to earn a place among the four clubs competing for a place in the play-offs.