Bobby Zamora gave Albion a massive boost for today's potential promotion clincher at London Road by returning a game early.
The prolific striker's dislocated shoulder was expected to keep him out of action until next Saturday's final home game of the season against Swindon.
But Zamora was back in the starting line-up for Peter Taylor's table-topping Seagulls.
Lee Steele also returned to partner Zamora following his dramatic stoppage time winner as a substitute against Bristol City on Monday.
Paul Brooker, the player Steele replaced, recovered from his ankle injury so loan signing Wayne Gray and Nathan Jones dropped to the bench.
Peterborough, effectively safe from relegation, were unchanged following Monday's 2-1 defeat at Wigan.
Barry Fry's men went into the game fresh from a hat-trick of home wins as the Seagulls looked for the victory they needed to have a chance of going up this weekend.
They were roared on by 3,300 fans who made the journey up the M11 in the hope of seeing their heroes seal back-to-back promotions.
Peterborough: Mark Tyler; Dennis Pearce, Marc Joseph, Andy Edwards, David Farrell, Andy Clarke, Francis Green, Jimmy Bullard, Leon McKenzie, Helgi Danielsson, Richard Forsyth. Subs: Oldfield, Gill, Fenn, MacDonald, Luke Steele.
Albion: Michel Kuipers; Paul Watson, Kerry Mayo, Danny Cullip, Simon Morgan, Junior Lewis, Gary Hart, Paul Brooker, Richard Carpenter, Lee Steele, Bobby Zamora. Subs: Oatway, Gray, N. Jones, Pethick, C. Jones.
Referee: Mr G. Frankland (Middlesbrough).
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