The visitors took the lead shortly before the half hour mark through Jack Payne, but Grant Holt was on target for Dale before the interval to ensure the teams went into the break on level terms.
A rampant Rochdale emerged for the second half, dominating the match and scoring a further three. Joe Raffery sent Keith Hill’s side in front four minutes after the re-start, before Jamie Allen lashed a wonderful long range effort beyond Dan Bentley shortly after the hour. Substitute Joe Bunney rounded off the scoring in stoppage time.
The wins moves Dale up to eighth in the table, just two points off the play-off places.
Hill made one change to the side lined up against Oldham Athletic for the Easter Monday clash. Grant Holt started in place of the suspended Ian Henderson.
Rochdale enjoyed plenty of the ball during the opening exchanges after starting the match brightly, but despite plenty of positive play, clear cut opportunities were at a premium as the game evened out.
Opportunities were also few and far between for the Shrimpers, who failed to test Josh Lillis for much of the half.
The visitors went on to open the scoring with their first real chance of the game in the 28th minute.
A Dale mistake allowed Anthony Wordsworth to feed the ball through to Jack Payne, who lifted the ball over Lillis with a neat finish.
Rochdale showed great character and continued to push for a goal. McDermott sent an effort wide of the upright from distance before Dale netted a deserved equaliser shortly before half time.
Michael Roses’ low cross from the left was touched by Camps into the path of Holt, who slid in to smash beyond Bentley.
A couple of minutes after the goal Bentley was forced into a save to keep out Rose, who struck a powerful effort from distance.
HT: ROCHDALE 1-1 SOUTHEND UNITED
Rochdale started the second half on the front foot and within two minutes of the re-start Nathaniel Mendez-Laing was denied by the underside of the bar. Holt’s delivery was met by Mendez-Laing, whose effort from close range crashed off the underside of the bar and back into play.
Dale didn’t let that deter them, though, and couple of minutes later they were ahead through Joe Rafferty. McDermott’s low ball across the face of goal was left by Camps for the full-back who finished beyond Bentley.
The visitors looked to find a way back into the game but were left frustrated as dominant Rochdale defended resolutely and kept opportunities at a minimum.
Dale, themselves, continued to show an attacking prowess and looked dangerous every time they came forward. They deservedly added a third through Jamie Allen shortly after the hour mark.
Jim McNulty laid the ball off for Allen, who lashed a wonderful strike from 20-yards into the back of the net.
Peter Vincenti replaced Mendez-Laing in the 71st minute and was involved straight away as he rifled a powerful strike at goal from distance. He was denied only by the finger-tips of Bentley, who sent the rasping effort round the upright.
Southend’s best chance of the half fell to Adam Barrett in the 81st minute when Payne crossed into the area from the left. He could only blaze his effort over the bar.
Allen saw an effort from 20-yards deflected narrowly wide of the target in the 87th minute, before substitute Bunney netted Dale’s fourth a minute into stoppage time.
His initial effort was kept out by Bentley, but he made no mistake as he smashed the rebound into the back of the net.
Andy Cannon replaced Callum Camps deep in stoppage time as Rochdale saw the game out.
FT: ROCHDALE 4-1 SOUTHEND UNITED