Suspension ravaged Mansfield hung on for a vital victory to boost their promotion hopes and deprive unlucky Southend of a first league win in four games.
The Stags, missing five banned key players, snatched a controversial early lead through their ninth successful penalty of the season and then rode their luck as Southend squandered a glut of golden chances.
United's best opportunity to salvage a point came in the 66th minute. Leon Constantine's close-range shot was blocked by keeper Kevin Pilkington and as the rebound flew up invitingly to Steven Clark he somehow miss hit his shot out for a throw in with the goal gaping.
Mansfield, playing mainly on the breakaway, twice went close to securing victory in the final stages, but both times Iyseden Christie fired narrowly wide.
Afterwards Mansfield manager Keith Curle said: "Today we had to face up to the ugly side of the game, give that little bit extra to get in the vital blocks. We had to match Southend's work rate commitment and desire, which all bely their position in the league." Curle had handed a fourth start of the season to teenage defender Alex Jean-Baptiste in centre-midfield in a completely reshaped line-up.
But it took the home side just three minutes to create the first chance, Neil Mackenzie firing a 20-yard drive into the side netting.
Nine minutes later Mansfield were in front. Christie raced onto a misplaced header and when he was brought down by keeper Darryl Flahavan, Wayne Corden converted the spot kick.
Ironically, the goal inspired Southend and they went on to dominate the rest of the match. Their first clear chance to equalise came in the 21st minute when Mark Gower cleverly controlled Duncan Jupp's deep cross, jinked inside a defender only to see his powerful shot deflected over the bar.
In the 39th minute, the impressive Gower robbed teenage full-back Jake Buxton and found Constantine, who neatly skipped past two defenders before curling his shot inches wide.
Just before half time, Leon Cort headed wide from a well-rehearsed corner routine, inevitably involving Gower.
Five minutes into the second half, Drewe Broughton repeated Southend's wastefulness in front of goal, somehow heading Clark's right-wing cross wide at the far post.