Blues shocked the League One leader's Wigan Athletic with a 3-1 win against the Latics at Roots Hall thanks to goals from Michael Turner, Marc-Antoine Fortune and Michael Kightly.
Turner nodded Southend in front inside the first three minutes after being picked out by a Stephen McLaughlin free-kick before Fortune doubled Blues’ lead with a neat finish.
James Vaughan was brought on as a substitute midway through the second half and reduced Southend’s lead almost immediately as he got on the end of a cross from Nathan Bryne to score.
The goal made for a nervy ending to the game but the pressure on the home side was lifted when Simon Cox’s effort was parried into the path of Michael Kightly who scored Blues’ third.
The win was Southend’s third in a row under new boss Chris Powell who became the first permanent Blues boss ever to win his opening three games in charge at Roots Hall.
Powell had already become the first Southend manager in 25-years to win his opening two games and the Blues boss made just one enforced change to his side that won at Peterborough.
Wigan came to Roots Hall looking for a club record seventh straight away league win but the league leaders were rocked by an early Southend United goal in just the third minute of the game.
After Stephen McLaughlin won Blues a free-kick by the corner flag, the Irishman’s cross into the area missed everyone in the centre of goal before Michael Turner popped up at the far post to head in.
Having gone behind early on, Paul Cook’s side responded well and had a great chance to level when a poor Anton Ferdinand clearance fell to Nick Powell who flashed wide from 12-yards out.
And just after the half-hour mark, a poor foul by Ferdinand on Powell resulted in a free-kick which was struck well by Max Power and had to be punched away from danger by Oxley.
Blues looked set to see the lead through to the break, but they were soon in dreamland when they doubled their advantage with Marc-Antoine Fortune scoring a well-worked Southend goal.
Cox picked the ball up from the left before playing a superbly weighted reverse pass into the run of the Frenchman who had the composure to slot the ball beyond Christian Walton to make it 2-0.
Not since mid-November against Bradford had Wigan tasted defeat and Blues could have been out of sight before the interval had Cox not blazed over Ben Coker’s low cross late on in the half.
Southend carried that forward momentum into the second half and created three great chances to extend their lead in quick succession early on.
A Blues break would lead to Fortune playing McLaughlin in, with his cross having to be cleared from underneath his own crossbar by Dan Burn.
From the resulting corner, a Ferdinand strike beat Walton but again cleared by Burn before Michael Kightly had a chance that he scuffed wide after being teed up by Fortune.
Wigan were finding it hard to deal with Southend’s intensity as they pressed the Latics at every possible moment in bleak, wet conditions in the South East.
Cook made a double substitution with half an hour to play with Gary Roberts and James Vaughan coming on and both almost combined to make an immediate impression on the game.
Roberts wiggled his way through two Southend defenders before seeing his cross frantically cleared for a corner and from the resulting set-piece, Vaughan was found unmarked only to head over.
Vaughan though would make up for that miss just moments later as he halved the deficit for the visitors, getting on the end of a low cross from Byrne to prod home with over 20 minutes remaining.
The pressure was starting to build on Blues as they began to sit deeper and deeper as Wigan pressed for an equaliser, but that pressure was alleviated when Southend made the points safe with a third.
With seven minutes of normal time remaining, Cox’s low strike wasn’t held by Walton who parried the ball into the path of Kightly to pounce and put daylight between Blues and Wigan once more.
With two-goal lead restored it allowed Southend to introduce Shayon Harrison for his Blues debut on loan from Tottenham and he went within inches of marking his debut with a goal in injury time.
Seven minutes of added on time were signalled but the Latics couldn’t break Southend down for a second time to force a tense finish as Blues made it three successive wins.
Blues XI: Oxley, Coker (C), Ferdinand, Turner, Kightly (McGlashan 90+5’), Timlin, Fortune (Ladapo 70’), Cox (Harrison 85’), McLaughlin, Yearwood, Demetriou. Subs Not Used: Bishop, Klass, Kyprianou, Bwomono
Wigan Athletic XI: Walton, Byrne, Elder, Morsy (C), Power, Grigg, Massey (Vaughan 61’), Jacobs (Roberts 61’), Dunkley, Powell (Colclough 87’), Burn. Subs Not Used: Jones, Perkins, Bruce, Fulton
Referee: Andy Woolmer
Assistants: Nigel Lugg & Akil Howsen
Fourth Official: David Spain
Southend United: Michael Turner 3’, Marc-Antoine Fortune 36’, Michael Kightly 83’
Wigan Athletic: James Vaughan 67’
Southend United: Anton Ferdinand 31’
Wigan Athletic: Nick Powell 43’, Chey Dunkley 47’, James Vaughan 90+3’