At half-time everything still seemed just possible, but even if Stoke hadn't won, Albion's 2-2 draw with Grimsby wouldn't have saved them.
And for a few tantalising minutes after the break, Brighton were 2-1 up at Blundell Park while Stoke and Reading remained locked in a goalless draw.
But the Seagulls had always been hanging by a thread. Stoke's Ade Akinbiyi scored for Stoke after 55 minutes.
Then on the hour, Grimsby's Richard Hughes sounded the death knell for Albion's First Division hopes. Stoke survive while the Seagulls face a season back down in the second.
The first half gave Albion's fans little cause for comfort. Keane scored from the spot in a controversial penalty for Grimsby on 23 minutes and the Seagulls struggled to get back into the game.
Only in injury time did top scorer Bobby Zamora level the field, again from a penalty.
And a minute into the restart came a dramatic turnaround as Albion captain Danny Cullip pounced from close range to take the lead.
The celebrations weren't to last.
In the 59th minute, Albion fans - already rattled by Stoke's lead against Reading at the Britannia Stadium - were silenced as the home side equalised.
Beasant parried a volley from Keane but Hughes, unmarked, was placed to tip the ball over the line from close range.
Grimsby: Coyne, McDermott, Santos, Chettle, Gallimore, Campbell, Richard Hughes, Groves, Keane, Mansaram, Thompson. Subs: Parker, Rowan, Bolder, Cooke, Pettinger.
Albion: Beasant, Blackwell, Cullip, Watson, Mayo, Ingimarsson, Rodger, Jones, Zamora, Kitson, Hart. Subs: Oatway, Brooker, Carpenter, Packham, Barrett.
Referee: C Wilkes (Gloucestershire)
More reports and analysis tomorrow
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