Blues won their fourth game in a row with a hard-fought win over ten-man Shrewsbury Town at Roots Hall in Sky Bet League Two.
Shaq Coulthirst's early strike proved the difference between two sides in the play-off places as Southend United's superb form continued.
Phil Brown named an unchanged starting XI to the one that beat York City just a week earlier, with Barry Corr remaining on the bench after his recent neck injury.
It was to be a terrific start for Blues – aiming to continue their superb form – and after only two minutes, Southend took the lead through Coulthirst.
The Tottenham loanee rose highest to float a terrific header past the despairing dive of Jason Leutwiler and into the bottom corner of the net.
Blues could have made it 2-0 just moments after the opener when a delightful cross from Kevan Hurst found the head of Coulthirst but Leutwiler did brilliantly to deny the Blues goalscorer.
At the other end, visiting striker James Collins fired just past Dan Bentley's right-hand post soon after, whilst Shrewsbury hit the upright moments later through Jean Louis Akpa Akpro. It was a manic opening ten minutes at Roots Hall.
After a frantic opening 20 minutes, the game died down a little but Luke Prosser did excellently to stop the marauding Mickey Demetriou having a shot on target after a string run forward.
Late into the half, a cross from the right by Myles Weston found Coulthirst lurking at the back post again but once more, Leutwiler was out to deny the Blues striker.
After the break, Blues looked to grab a second and on 53 minutes, Weston burst through but his strike was saved by Leutwiler and the follow up effort his over the crossbar by Conor Clifford.
Just before the hour mark, a dinked ball into the box from Hurst found Williams, but his glancing header went just past the post.
With 20 minutes remaining, Akpa Akpro saw his header fall onto the roof of Bentley's net from a Jordan Clark cross from the left side.
Corr made his return to action on 74 minutes and moments later saw his header from a Weston cross saved by Leutwiler.
Four minutes later and Blues had another chance when Coulthirst picked out Weston, but the winger's effort went into the side netting. At the other end, Ashley Vincent's effort was held by Bentley.
With ten minutes of the game remaining, Blues were really looking to kill the game off and Corr saw his strike fly over the bar from an acute angle.
There was to be late drama for Shrewsbury when, with seven minutes left, substitute Andy Mangan looked to get on the end of a long punt upfield but Bentley got to the ball first and the aerial collision between the two led to Mangan being shown a second yellow card.
Despite the referee adding on six minutes of extra time, Blues held on for another valuable three points.
Blues: Bentley; White (C), Thompson, Prosser, Williams; Payne (Corr, 74), Deegan, Clifford; Hurst (Atkinson, 63), Weston (Bolger, 90), Coulthirst
Un-used: P. Smith, Ibenfeldt, Barnard, Bridge