Alan McCormack returned from suspension to score a dramatic winner at the death and send Southend towards a crucial 2-1 victory at Huddersfield Town.
As things previously stood a draw would have sent the Blues out of the top six of League One, but instead the three points gained now pushes the club up to fifth in the table.
Southend dominated the early exchanges, applying firm pressure in the final third and enjoying a high succession of corners.
It was through one of these that Adam Barrett supplied the first serious threat when he rose highest to win the ball, but the captain's header sailed on to the roof of the net.
A brilliant turn from Mark Gower outside the box helped him find a sight of goal, but with perhaps more time than he thought, the winger drilled the ball straight at goalkeeper Matt Glennon.
Michael Collins nearly found a free route to goal after bypassing the challenge of Barrett, but he played the ball too far forward in the process and allowed Darryl Flahavan to rush out to smother possession.
The Blues continued to impress with Tommy Black sliding James Walker into the box and the young striker shaped to shoot with a fierce effort into the side netting.
Yet five minutes before the interval and Southend took the lead they deserved.
Black played the ball to Hal Robson-Kanu on the edge of the box and the on-loan frontman did the rest in shuffling past his marker and rifling a left-foot shot past Glennon for his second goal in two games.
Chances were at premium in the second half with the Blues having to display more grit at the back, as less space was being presented in their favour at the other end of the field.
Huddersfield became more involved as the game progressed with Jon Worthington presented with the ball inside the box, but hitting a low effort straight into the arms of Flahavan.
Southend had done their best to mute the hosts threat, but they failed to deal with a 73rd minute corner and Andy Booth was first to react to plant a powerful header past Flahavan.
Malvin Kamara knocked a late Barrett header off the line, but McCormack went on to have the last word of the match deep into stoppage time.
The Irishman raced on to a long ball forward and kept his composure to send a low shot past Glennon and into the net via the post for his ninth goal of the season.
Southend: Flahavan, Francis, Clarke, Barrett, Mulgrew (Grant 35), Black (Moussa 78), McCormack, Bailey, Gower, Robson-Kanu (Barnard 78), Walker.
Huddersfield: Glennon, Holdsworth, Collins (Broadbent 79), Clarke, Brandon, Worthington (Berrett 86), Williams, Sinclair, Kamara, Booth (Beckett 79), Page.
