Grimsby 2-2 Brighton
Zamora scored from the spot
Brighton saw their hopes of escaping relegation slip through their fingers at Blundell Park.
The Seagulls needed a win away to Grimsby and hope that Stoke lost at home to Reading to avoid dropping back into Division Two, but neither result went to plan.
In the end Brighton's result made no difference as Stoke secured three points against the Royals.
Grimsby went into the game with little to play for, with relegation already decided and the Mariners sure to finish bottom of the table.
But they showed they were not about to make life easy for Brighton, who were backed by an army of 2,500 noisy fans, some of them in fancy dress.
Tony Gallimore drilled in a free-kick that took a deflection and needed Dave Beasant to react quickly to keep the shot out with his legs, before Stuart Campbell fired over from the rebound.
HOW THE BOTTOM STANDS
22. Sheff Wed 46 pts
23. Brighton 45 pts
24. Grimsby 39 pts
The home side took the lead midway through the opening period in controversial circumstances.
Brighton defender Kerry Mayo brought down Chris Thompson and while there was little doubt about it being a foul, the challenge looked to be outside the box.
Michael Keane, on loan from Preston, sent Beasant the wrong way from the spot.
Grimsby went close to adding a second when Richard Hughes found space in the area and fired in a left-foot shot, but Beasant got down well to hold onto the ball.
Brighton struggled to get anything going in the opening half with Grimsby coping much better in the blustery conditions.
Bobby Zamora had to wait until the stroke of half-time for his first meaningful contribution.
He cut inside from the right and attempted to curl one into the far corner but his left-foot shot finished well wide.
In first half injury time Zamora, almost certainly playing his final game for the club, got the equaliser.
Gary Hart tricked his way into the area and was upended by veteran defender Steve Chettle.
23 mins: A Keane penalty puts Grimsby in front
45 mins: Zamora equalizes from the spot
47 mins: Cullip gives Brighton the lead
60 mins: Hughes puts Grimsby back on level terms
Referee Clive Wilkes pointed straight at the spot for a second time and Zamora kept his nerve to sidefoot past Mariners stopper Danny Coyne.
It was the Seagulls' first attempt on target and allowed their fans to spend half-time dreaming of mission impossible.
The edged another step towards their safety goal when they went in front through Danny Cullip.
The big defender bundled home from close range for his first goal in 39 games.
But as news Stoke had gone ahead at the Britannia Stadium filtered through, Grimsby grabbed a leveller.
Player of the season Danny Cullip is mobbed by fans
Beasant did well to push out Keane's initial volley but Hughes was on hand to finish from point-blank range.
Keane incensed the travelling supporters with his celebrations but stewards prevented a pitch invasion.
Brighton appeared resigned to their fate and Grimsby almost added a winner when Thompson saw a shot come back off the woodwork.
Grimsby: Coyne, McDermott, Santos, Chettle, Gallimore, Campbell, Richard Hughes, Groves, Keane, Mansaram, Thompson.
Subs: Parker, Rowan, Bolder, Cooke, Pettinger.
Brighton: Beasant, Blackwell, Cullip, Watson, Mayo, Ingimarsson, Rodger, Jones, Zamora, Kitson, Hart.
Subs: Oatway, Brooker, Carpenter, Packham, Barrett.
Referee: C Wilkes (Gloucestershire).