Southend snatch all three points as Dons' poor run goes on
Karl Robinson's men went into the game confident of claiming their first victory on home soil since March, but things started badly and got steadily worse.
Simon Cox fired the visitors into a second-minute lead, and Southend were 2-0 up after 24 minutes thanks to a strike from Anthony Wordsworth.
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Hide AdDons enjoyed plenty of possession, and had chances to get back into the game, but they failed to take them.
Southend then rubbed salt into the Dons' wounds when Wordsworth scored his second and the visitors' third in stoppage time.
There were three changes to the MK team from Tuesday night's 3-3 draw with Bristol Rovers as Joe Walsh, Darren Potter and Daniel Powell all started.
They replaced the suspended Dean Lewington, Ed Upson and the injured Kieran Agard (knee).
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Hide AdSouthend got their afternoon off to a flyin start when former Republic Of Ireland striker Cox fired past Dave Martin after Dons failed to clear a corner.
Ben Reeves then brought a fine save from Mark Oxley, who then made a great double save on 14 minutes to deny Walsh and Potter.
It was somewhat against the run of play when Wordsworth made it 2-0, firing home clinically from 15 yards.
Reeves was wide with a free-kick while Dean Bowditch also went close, while Martin made a good stop to deny Will Atkinson and keep his team in the game.
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Hide AdDons needed a good start to the second half, but they couldn't find the breakthrough they needed despite efforts from Samir Carruthers, and on 73 minutes Bowditch again went close, but this time his effort went over the bar.
Dons became increasingly frustrated as the clock ran down, and Wordsworth made sure of a great away day for Southend with a 25-yard free-kick in stoppage time.
The defeat means Dons have claimed one point from the past 12 available to them, and they are now 19th in Sky Bet League One, just a point above the relegation zone.