Rejuvenated Mark Wright scored twice as MK Dons gave their automatic promotion hopes a boost and all but knocked Southend out of the playoff race.
Wright struck twice in the second half as the depleted Dons produced a defiant display to close the gap on promotion rivals Millwall and Peterborough.
Without top scoring trio Aaron Wilbraham, Sam Baldock and Peter Leven through injury, the Dons were always going to be in for a battle against a Shrimpers side with five wins in their last six. But thanks to some heroic defending, some wonderful goalkeeping from Willy Gueret and Wright's clinical finishing, Roberto Di Matteo's men were able to kick off the crucial Easter weekend with a big win.
Having spent nine weeks out of the side before last week's victory over Brighton, Wright has taken his chance with both hands in the last two games. Wright curls home his and the Dons' second in injury time at Roots Hall.
While last week's assist for Jason Puncheon's clinching second against the Seagulls was impressive, the Wright at Roots Hall was the gun-slinging winger whose 15 goals fired the Dons to the League 2 title last season. Unrestricted to his flank and with the knack of finding scoring space inside the box, Wright's goals - his first a diving header from Stephen Gleeson's cross on the hour and his second a sumptuous finish from another Gleeson pass in injury time - left Southend's playoff challenge in tatters.
The home side had started like a team in form and went close twice in the opening exchanges. Striker Theo Robinson tried to catch out Gueret with a well-struck volley on three minutes but found the Frenchman too big an obstacle to pass. Franck Moussa followed that up by dragging a shot wide when well placed on 18. Damian Scannell hooks away from Stephen Gleeson.
But the Dons gradually found their feet - Gleeson and Luke Howell starting to hold their own in the midfield battle and Puncheon starting to see more of the ball ahead of them. It started to look promising for the visitors and when Gleeson's clever pass found Puncheon on the right edge of the box, the on-loan Plymouth man put Wright into shooting space.
Wright got his shot off and must have been celebrating when it broke kindly to Chadwick just six yards from goal. But as the former Manchester United man brought the ball under control he was knocked off balance and couldn't provide the simplest of finishes. It was a big let-off for the home side, but the Dons continued to up the pressure and when Puncheon stayed on his feet despite being tugged back by Peter Clarke a minute later, his stinging drive was pushed over by Shrimpers 'keeper Steve Mildenhall.
Puncheon was involved again shortly before half-time when he and Ali Gerba combined to set up Gleeson, whose 25-yard shot deflected just wide. Just as they had in the first, Southend started the second half like a train and were within inches of taking the lead just two minutes after the restart. Damian Scannell's dangerous low cross from the right was instinctively, if not safely, flicked away by Sean O'Hanlon as he raced back towards his own goal. But when Lee Barnard fired the loose ball past Gueret, O'Hanlon was behind him to head off the line.
Gueret's impressive afternoon continued as he got down well to an Alan McCormack free-kick before scrambling the rebound away from Barnard with his feet. And the Frenchman was unbeatable once more on 57 minutes when McCormack's snapshot flew goalwards from just inside the box. The pressure was starting to mount on Di Matteo's side, but they produced a goal of real quality to ease it.
Anthony Grant had been the armour in front of the Southend defence for most of the game, but when Chadwick stripped the former Chelsea man away in midfield the home defence looked dangerously exposed. Chadwick fed Gleeson to his right, who drove a gorgeous first-time cross into the box for Wright to head superbly past Mildenhall.
The celebrations were wild among the 1,000 travelling supporters as Wright raced to thank Gleeson for the assist. It proved a mortal wound for Southend. Having created a number of chances before that, Southend looked short on energy and ideas after falling behind and couldn't find a way through a well-marshalled Dons defence.
The movement of Robinson and Barnard proved problematic for O'Hanlon and Miguel Llera early on, but under the high ball they were in their element. Moussa sliced a shot over after Gueret had punched a free-kick away under pressure and substitutes Dougie Freedman and Francis Laurent almost combined to great effect, only for the latter to scuff wide.
And when Gleeson launched a counter attack after O'Hanlon had headed a free-kick clear Southend were caught short at the back. Gleeson waited, Wright arrived and the finish was exquisite.
Southend United (4-4-2): Mildenhall; Francis, Dervite, Clarke, Barrett (c); Scannell (Betsy 77), Grant, McCormack, Moussa; Barnard (Freedman 75), Robinson (Laurent 75).
Subs not used: Sankofa, Christophe. Booked: Grant, McCormack.
MK Dons (4-2-3-1): Gueret; Regan, O'Hanlon, Llera, Lewington (c); Gleeson, Howell; Wright, Puncheon (Belson 89), Chadwick (Stirling 66); Gerba (Flo 71).
Subs not used: Abbey, Johnson.
Goals: Wright 59, 90+1.
Attendance: 10,241 (998 away).
Referee: Paul Taylor (Hertfordshire).