Cardiff gave Albion a boost last night by failing to win their game in hand.
Neal Ardley's 58th-minute equaliser earned the Bluebirds a 1-1 draw away to Leicester, who had Nikos Dabizas sent off in the closing stages.
The draw moved Lennie Lawrence's men a point clear of Albion and above Crewe.
Victory, though, would have put them three points clear of the Seagulls with a vastly superior goal difference.
Now Albion know they could overtake Cardiff providing they can win at least one of their remaining three games.
Cardiff, who had trailed to David Connolly's first-half strike, still have to play Reading at home, Gillingham away and then QPR at home on the final day.
Albion's search for a first victory in nine games begins at home to West Ham on Saturday.
They won 1-0 at Stoke last night to move to within a point of the play-off places.
Former Seagulls favourite Bobby Zamora, who makes his first return to Withdean on Saturday, scored the only goal of the game 12 minutes from time.
The goal came just two minutes after coming on as substitute for defender Tomas Repka.
Five teams - Watford, Coventry, Gillingham, Cardiff and Crewe - remain realistically within catching distance of Albion. Watford, perhaps, have the toughest run-in with three teams in the top half of the table to play.
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