Morecambe paid for a poor start as they exited the FA Cup at the first round stage on Saturday.
Two Anthony Straker goals inside the first 10 minutes handed Southend their first ever victory over the Shrimps at the eighth attempt.
It was then an even game after the shocking start for the hosts, but Ryan Leonard added some gloss to the scoreline in stoppage time for Phil Brown’s side.
It was the worst possible start for the hosts who went behind to the first attack of the game on seven minutes.
Former Shrimps loanee Kevan Hurst beat Robbie Threlfall down the Southend right and whipped in an inviting cross that was chested in from close range by Straker.
And the wide man had his second less than two minutes later, capitalising on a poor Morecambe throw-in, the visitors countered and Straker cut in from the left just outside the area and saw his shot deflect off the returning Chris McCready and go into the far corner leaving Barry Roche stranded.
Not content with two goals, Straker came close to a five-minute hat-trick but Roche rushed out to deny him after the Southend man had ghosted past three players down the left.
Morecambe settled but it was the visitors who came close to getting the game’s next goal on 24 minutes, Hurst again too good for Threlfall but his driven cross was just out of the reach of a sliding Barry Corr at the back post.
The Shrimps’ first clear-cut chance came on the half hour, stand-in skipper Andy Wright heading Ryan Williams’ corner narrowly wide at the near post as they finished the half strongly with Marcus Marshall a real threat down the right-hand side.
After the break, the Shrimps failed to turn early promise into chances as Southend continued to look a threat on the counter.
Roche had to be alert on 53 minutes to beat away a Corr effort before at the other end Williams had Dan Bentley scrambling with a 20-yard effort that flashed just wide on the hour mark.
The visiting ‘keeper was again called into action by the Shrimps number 10 two minutes later as he helped over a dipping 25-yard free-kick before doing the same to a vicious corner that looked to be heading straight in.
It was another Williams corner that presented Morecambe with a great chance 20 minutes from time, but McCready could only help the ball over the bar from six yards after it dropped in his favour on the half volley.
Southend came inches from settling things 15 minutes from time, Hurst’s shot from 20 yards going narrowly wide of the left-hand post.
Jack Sampson and Joe Mwasile were introduced to try and drag the hosts back into the game but despite plenty of endeavour the Shrimps never really looked like forcing a replay as Leonard settled things for the visitors in stoppage time with a low drive into the corner.
Morecambe: Roche, Wright (capt), Parrish (Diagne 90), McCready, Threlfall, Drummond, Fleming (Sampson 72), Williams, Marshall (Mwasile 76), Ellison, Amond. Subs not used: Arestidou, Kenyon, McGee, Doyle.
Booked: Fleming, Marshall, Ellison
Southend: Bentley, White (capt), Prosser, Kiernan, Coker, Leonard, Atkinson, Timlin, Straker, Corr, Hurst. Subs not used: Smith, Laird, Reid, Payne, Thompson, Auger, Woodrow.
Booked: Leonard, Atkinson
Referee: Rob Lewis
Attendance: 1,475 (159 Southend)