These two sides will meet again in the second division next season after a draw sealed Brighton's relegation fate.
Bottom of the table Grimsby were already relegated and to stay up Brighton had to win and hope that Reading would be successful at Stoke.
Neither result materialised but there was a good atmosphere at Blundell Park helped by 2,500 travelling Seagulls fans who did their best to bring about an unlikely salvation for their side.
The first half was a tale of two penalties. Firstly on-loan mid fielder Michael Keane sent Dave Beasant the wrong way on 21 minutes following a foul and then in first-half stoppage time Brighton's leading scorer Bobby Zamora gave the visitors hope by pulling them level.
And hope sprung eternal after two minutes of the second half when skipper Danny Cullip fired the Seagulls ahead when Grimsby failed to clear a corner.
But with the news that fellow strugglers Stoke were beating Reading there was even worse news for Brighton on the hour when on loan midfielder Richard Hughes marked his last game for the club with his first goal.
Both sides went for victory in the closing stages with Brighton looking the better bet although it was Grimsby who went closest with a stunning effort from striker Christopher Thompson which flew back off the angle.
Both sides used all three subs in a bid to force the issue with long-serving skipper John McDermott getting a tremendous ovation as he was replaced by Wes Parker in the final minute.
But the scoreline was just about right with Brighton returning to the second division after one season in the first and Grimsby joining after five seasons.