Chris Powell enjoyed a second-straight win since taking over as Southend United manager after an early Jason Demetriou penalty gave the Shrimpers a 1-0 win at Peterborough United.Demetriou fired in after just seven minutes after Peterborough goalkeeper Jonathan Bond caught the leg of Stephen McLaughlin inside the area.Posh had a few good chances and would have levelled if League One top-scorer Jack Marriott had taken either a decent headed chance or two one-on-one opportunities either side of half-time, with visiting goalkeeper Mark Oxley denying the striker on all three occasions.Southend central defender John White was carried off on a stretcher after injuring himself while attempting a tackle on Marriott, and - soon afterwards - Simon Cox and McLaughlin both narrowly fired wide for the visitors, who held on for a first away win since October.Peterborough began the day just four points outside the play-offs but could not find a way past Oxley despite 10 minutes of additional time being added on in the second-half, largely due to White's injury.