Erhun Oztumer’s second-half hat-trick earned Walsall a first away win of 2018 and ended Southend manager Chris Powell’s unbeaten start.
The Roots Hall contest only went ahead after Shrimpers ground staff and fans had cleared snow off the pitch before kick-off.
Powell’s side started the day unbeaten in five and enjoyed the better of the opening half-hour, Simon Cox threatening first with a near-post effort which keeper Liam Roberts held.
Freddie Ladapo headed over from Shayon Harrison’s left-wing cross and Cox directed a free header into the arms of Roberts, who also held a tame Cox chip.
Southend’s best chance of the first half came on 30 minutes, Dru Yearwood charging down George Dobson’s clearance before being denied by the onrushing Roberts.
The Saddlers ended the half the stronger, with Kieron Morris curling a left-footed effort inches wide and Julien Ngoy exchanging passes with Oztumer before bending a 20-yard shot past the post.
Ngoy went close again two minutes after the resumption, rolling Michael Turner superbly but his angled drive was blocked by the legs of Shrimpers keeper Mark Oxley.
The hosts had a big chance to take the lead on 49 minutes when ex-Saddler Jason Demetriou’s deep cross found Harrison unmarked but he volleyed wastefully over from close range.
After Maz Kouhyar had fired wide, the visitors broke the deadlock on 57 minutes when Oztumer’s left-footed 20-yard strike skidded off the surface and bounced over the dive of Oxley.
The diminutive playmaker struck again nine minutes later, whipping an accurate 25-yard free-kick into the bottom corner for his 15th goal of the season.
Walsall had chances to go further ahead, with George Dobson curling a free-kick over the bar and Oztumer seeing another set-piece effort parried by Oxley.
A third goal duly arrived with four minutes remaining, Luke Leahy delivering a pinpoint low cross for Oztumer to poke home and complete his first professional career treble.
Southend pressed late on but the Saddlers stood firm to perverse the clean sheet and send the 119 hardy away fans home happy.