Albion's destiny in the play-off race is back out of their hands after a 2-0 win for Reading at home to mid-table Middlesbrough.
Adam Le Fondre and an own goal by George Friend in the opening 14 minutes put the Royals in charge at the Madejski Stadium.
Reading are now a point and a place above Albion in sixth, with an identical plus 12 goal difference.
The Seagulls have the chance to move back above them by beating doomed Yeovil at the Amex on Friday evening.
The rest of the contenders are in action on Saturday, including Reading at relegation-threatened Doncaster Rovers.
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