Goals from Niall Canavan and Calvin Andrew gave Dale a half-time lead, before Nathaniel Mendez-Laing made sure of the points with six minutes left to play.
Dale, who have moved up to sixth in the Sky Bet League 1 table, are now unbeaten in eight games in all competitions.
There were four changes to the side that lined-up against Notts County in Tuesday night’s Checkatrade Trophy group stage tie.
Keith Keane, Joe Bunney, Calvin Andrew and Steven Davies all returned to the starting eleven. 16-year-old Aaron Morley, who made his debut in the EFL Trophy game, was handed his first league start for the club. In the absence of Jamie Allen (knee injury) and Ian Henderson (concussion), Academy graduate Callum Camps wore the captain’s armband.
Dale had the first half chance of the game, when Bunney whipped a dangerous ball into the area. Andrew headed wide of the upright.
It was a sign of things to come and Rochdale opened the scoring in the 18th minute from a set-piece. Bunney’s delivery from a free-kick was met by the towering Canavan, who powered a header beyond Mark Oxley at the back post.
An enforced substitution followed immediately, as the injured Joe Thompson was replaced by Nathaniel Mendez-Laing.
Soon after, the visitors had the ball in the back of the net through David Mooney, but his goal was ruled out for off-side.
Dale were in control and Mendez-Laing tested Oxley from distance, before Andrew doubled the advantage. After the Shrimpers could only partially defend away a Rafferty corner ball, the full-back regained possession and delivered back into the area for Andrew to head home.
On the half hour mark, Morley forced Oxley into a save, with the ‘keeper pushing the on target effort from the edge of the area wide of the target.
The visitors grew into the game without truly troubling and it was Dale who finished the half strongly.
Andrew fired wide of the upright after getting his shot away, despite being closed down, while Mendez-Laing’s low cross from the byline was blocked and defended away just a couple of yards from the goal line.
HT: ROCHDALE 2-0 SOUTHEND UNITED
After the break, Rochdale had the first opportunity of the second half. Mendez-Laing, who raced to the byline, delivered low across the face of goal, but Andrew, who came sliding in at the back post, couldn’t make a connection.
A couple of minutes later, Lillis, who was rarely threatened during the game, was called into action, as he rose highest to punch away a delivery from Ben Coker before substitute Nile Ranger, who was lurking at the back post, could get on the end of it.
Morley, who appears older than his years due to his intelligent footballing play, came within inches of netting a stunning effort on his league debut. The youngster showed great maturity as he struck a curling effort, which had beaten Oxley, at goal. It looked almost certain to nestle in the top corner of the net, but went narrowly wide of the right.
Soon after, Morley received a standing ovation as he made way for Ollie Rathbone in the 69th minute.
Rochdale had been in control throughout the game and they put it out of sight in the 84th minute. Mendez-Laing raced in on goal and struck beyond the out rushing goalkeeper to net Dale's third of the afternoon.
FT: Rochdale 3-0 Southend United