SHEFFIELD United’s play-off hopes were dealt another blow as Peter Vincenti and Grant Holt came off the bench and scored the goals at Spotland.
But the other Rochdale hero was goalkeeper Josh Lillis, who made five top saves to deny Nigel Adkins’s side.
The Blades made one enforced change with Belgian Florent Cuvelier stepping into midfield for the banned Dean Hammond.
Rochdale also made one change from the side which defeated Fleetwood in midweek, former Blades loanee Nathaniel Mendez-Laing replacing ex-Barnsley striker Reuben Noble-Lazarus.
The Blades almost took an eighth-minute lead when Lillis tipped over a 12-yard volley from Cuvelier and then Martyn Woolford’s inswinging corner flicked off a defender’s head but against the far post.
Lillis repeated his save from Che Adams’s volley from outside the area and also denied the Blades striker with a block from a low drive close to the break.
Before that, the Blades had lost Woolford to an ankle injury sustained in a late tackle from Matt Lund and former Dale striker Matt Done replaced him.
Rochdale rarely threatened and captain Ian Henderson headed wide their best chance before the interval when the sides went in level at 0-0.
Rochdale made two changes for the second-half, experienced duo Vincenti and Holt replacing Joe Bunney and Mendez-Laing.
Lillis was at it again as he smothered the ball at the feet of Billy Sharp before the Blades were stunned as Holt and Henderson combined to set up Vincenti, who curled home a 67th-minute shot from the edge of the area beyond George Long, diving to his left.
Adams almost equalised but his shot into the ground was pushed away for the Blades’ ninth corner by Lillis.
The Blades brought on Paul Coutts and Stefan Scougall for Cuvelier and Ryan Flynn in the 75th minute in an attempt to get back in the game.
However, it was Rochdale who made it 2-0 in the 81st minute, Holt, recently returned to the club after being released by Wigan, sweeping home Michael Rose’s inswinging delivery.
Understandably, Blades fans vented their fury at their side’s inability to get back in it, police and stewards having to control a particularly rowdy section.
Dale finished well on top.
Blades boss Nigel Adkins said: “I thought we were dominant, I thought we were on the front foot. It was a lively pitch but no excuses there.
“I thought we played forward and created chances and had energy about ourselves but it’s about scoring goals and unfortunately their goalkeeper was very, very inspired.
“Even in the second half I thought we started brightly enough, we had chances in the second half and that’s probably with their first chance that they have gone and scored.
“There was a melee in the penalty area and our players lost the goalscorer for them. He’s got a free shot at goal, he goes and scores and that makes it more challenging for us.
“We’ve come here to win a game and for a good hour we were on the front foot, trying to impose ourselves to make that happen.
“But it’s about results and I can’t explain it any more than that.”