Southend’s hopes of making the Enterprise National League play-offs were dealt a blow as Liam Humbles struck in the first half to earn Altrincham a 1-0 home win.
The midfielder scored in the 14th minute to win it, reacting first to prod the ball home after goalmouth scramble.
Alty goalkeeper Luke Hutchinson produced quick-fire saves early in the second half from Harry Boyes and Joe Gubbins.
Victory moved Altrincham to 14th while seventh-placed Southend now hold just a two-point advantage over Halifax.
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