Fulham loanee Cauley Woodrow netted a 76th-minute winner as Southend made AFC Wimbledon pay for George Francomb's first-half dismissal with a 1-0 victory at Kingsmeadow.
Woodrow powered a header home from John White's cross after Dons midfielder Francomb was shown a straight red card for a hard tackle on Robert Kiernan.
It appeared as if the Dons would hold on with Southend creating little after the break but Woodrow, a 59th-minute substitute for Ryan Leonard, earned the Shrimpers' first league win in four outings.
Francomb had the Dons' best chance of the first half when he forced Southend goalkeeper Daniel Bentley to tip a curling effort wide - but his 41st-minute dismissal was to prove costly.
Southend were limited to long-range efforts in the first half but Wimbledon keeper Ross Warner did well to keep out Kevan Hurst's 25-yard effort.
The Dons started the second half strongly and Michael Smith's strike from long distance was deflected over the crossbar after nice work from Jack Midson.
Southend's extra player soon began to tell though, and Woodrow sealed the win 14 minutes from time while Midson was thwarted by visiting defender Mark Phillips at the death.