Jamal Campbell-Ryce struck twice as Southend threw the form book out of the window to secure a vital 3-1 victory against in-form West Brom.
The winger had failed to score a single goal for the Championship's basement side prior to the visit of promotion-chasing Albion, but he produced two superb first-half finishes against Tony Mowbray's men.
Former Derby defender Lewis Hunt then headed a third for the home side five minutes before the break to stun the visitors, who had gone six games without defeat prior to their trip to Roots Hall.
Substitute John Hartson pulled a goal back for Albion just after the hour, but it proved to be no more than a consolation as the Shrimpers boosted their hopes of avoiding the drop by claiming three precious points.
Defeat for West Brom leaves them without a victory on their travels since the 2-0 success at Crystal Palace on October 17.
The Baggies started brightly and forced two early corners, but it was Southend who broke the deadlock 11 minutes in with the goal coming from an unlikely source.
Campbell-Ryce picked up a loose ball 25 yards from goal and unleashed a venomous right-foot strike that flashed past Russell Hoult and found the bottom the corner of the net.
Then just before the half hour Campbell-Ryce doubled the home side's advantage with another clinical finish.
Lee Bradbury was the architect, cushioning a neat header into the path of the 23-year-old winger who smashed the ball home from 20 yards out.
Albion looked vulnerable in defence and they were punished once again when Hunt rose highest to nod home Mark Gower's pinpoint cross.
The Baggies' leading scorer Diomansy Kamara almost pulled a goal back a minute before the interval but his left-foot drive was superbly kept out by the agile Darryl Flahavan.
Mowbray boldly made a triple substitution at the break, with Zoltan Gera, Martin Albrechtsen and Kevin Phillips replaced by Nathan Ellington, Neil Clement and Hartson.
Just as in the first half, Albion started the second 45 minutes positively, with Jason Koumas trying his luck with a long-range free-kicks, but failing to test Flahavan.
Then former Manchester United midfielder Jonathan Greening also failed to hit the target with a powerful strike from 25 yards out.
With the visitors committing men forward Southend were always likely to be dangerous on the break and they almost scored a fourth goal when Freddy Eastwood crossed for Adam Barrett, whose header produced a fine save from Hoult.
A scrappy period of play ensued, but Albion were thrown a lifeline when Hartson bundled home Darren Carter's inswinging corner with 62 minutes on the clock.
Some resolute Southend defending frustrated Mowbray's men and they began to lose their discipline with Robinson, Paul McShane and Carter joining Greening and Phillips in the referee's notebook.
To their credit, Albion continued to press and Koumas flashed a vicious left-foot strike narrowly wide of Flahavan's left-hand post with eight minutes remaining, but the hosts comfortably held out.
The winger had failed to score a single goal for the Championship's basement side prior to the visit of promotion-chasing Albion, but he produced two superb first-half finishes against Tony Mowbray's men.
Former Derby defender Lewis Hunt then headed a third for the home side five minutes before the break to stun the visitors, who had gone six games without defeat prior to their trip to Roots Hall.
Substitute John Hartson pulled a goal back for Albion just after the hour, but it proved to be no more than a consolation as the Shrimpers boosted their hopes of avoiding the drop by claiming three precious points.
Defeat for West Brom leaves them without a victory on their travels since the 2-0 success at Crystal Palace on October 17.
The Baggies started brightly and forced two early corners, but it was Southend who broke the deadlock 11 minutes in with the goal coming from an unlikely source.
Campbell-Ryce picked up a loose ball 25 yards from goal and unleashed a venomous right-foot strike that flashed past Russell Hoult and found the bottom the corner of the net.
Then just before the half hour Campbell-Ryce doubled the home side's advantage with another clinical finish.
Lee Bradbury was the architect, cushioning a neat header into the path of the 23-year-old winger who smashed the ball home from 20 yards out.
Albion looked vulnerable in defence and they were punished once again when Hunt rose highest to nod home Mark Gower's pinpoint cross.
The Baggies' leading scorer Diomansy Kamara almost pulled a goal back a minute before the interval but his left-foot drive was superbly kept out by the agile Darryl Flahavan.
Mowbray boldly made a triple substitution at the break, with Zoltan Gera, Martin Albrechtsen and Kevin Phillips replaced by Nathan Ellington, Neil Clement and Hartson.
Just as in the first half, Albion started the second 45 minutes positively, with Jason Koumas trying his luck with a long-range free-kicks, but failing to test Flahavan.
Then former Manchester United midfielder Jonathan Greening also failed to hit the target with a powerful strike from 25 yards out.
With the visitors committing men forward Southend were always likely to be dangerous on the break and they almost scored a fourth goal when Freddy Eastwood crossed for Adam Barrett, whose header produced a fine save from Hoult.
A scrappy period of play ensued, but Albion were thrown a lifeline when Hartson bundled home Darren Carter's inswinging corner with 62 minutes on the clock.
Some resolute Southend defending frustrated Mowbray's men and they began to lose their discipline with Robinson, Paul McShane and Carter joining Greening and Phillips in the referee's notebook.
To their credit, Albion continued to press and Koumas flashed a vicious left-foot strike narrowly wide of Flahavan's left-hand post with eight minutes remaining, but the hosts comfortably held out.
