The Blades picked up four points over the Easter period but Unitedites left the Lane disappointed after Monday's goal-less draw.
It was United's third successive scoreless draw at home but the persistent pressure could not breakdown Carlisle's resilient rearguard.
Liam Noble hit a post for Carlisle, who had Sean O'Hanlon sent off in the second half.
With Flynn picking up an ankle problem in the last fixture, loanee Poleon was given a start and Murphy returned to the bench. Carlisle's team included former Blades McGovern and Thirlwell, with Cadamarteri on the bench.
Kick-off saw Poleon on the left, a straight swap for Flynn, allowing Robson to stay wide on the right and Forte and Kitson to operate centrally.
Despite the sun shining, a slow start failed to ignite the crowd. For the visitors Miller beat the offside trap but was denied by a combination of Hill and Doyle, whilst Welsh headed wide a deep cross from Simek, United's offerings were a McDonald shot that was blocked and a Poleon header, although he was called offside.
A number of set-pieces, free-kicks in dangerous positions, and corners, failed to get the Blades off the mark, although goalkeeper Gillespie was tested by a near post effort from Robson and Maguire appeared to be hauled away as he attempted to meet another.
Long had to be well positioned when Welsh found space for a shot on 22 minutes, whilst United were quickly back on the offensive with Collins heading from close range after another Robson corner.
On the half hour, McMahon was the first to be shown a yellow card, following a discussion between the referee and one of his assistants, but the Blades continued to force Carlisle back. McDonald's first-time, lashed half-volley was pushed away by Gillespie, whilst Robson was just wide with a shot from the edge of the box.
The best chance of the half was the last one and it came from the visitors. The Blades failed to clear a move down Carlisle's left and Noble's half-volley from the edge of the box struck Long's left post before being hacked away to safety.
Kicking towards the Kop in the second half, the home side made a double change with Higginbotham and Murphy replacing Hill and Poleon. Murphy was quickly involved, delivering an inviting cross which Robson almost got on the end of.
Doyle fired wide with his unfavoured right foot before the Blades made a final change just after the hour, Ironside taking over from Kitson. Once again the substitute almost made an instant impact, the teenage striker doing exceptionally well to hold up the ball before laying off for Forte to scuff wide.
In a rare attack from the visitors, O'Hanlon headed just wide a cross on 71 minutes and it turned out to be his last positive contribution as soon after he was shown a yellow card for his foul on Ironside. It was the Carlisle central defender's second booking and he disappeared down the Lane tunnel.
Murphy's run down the right caused problems for the ten men and a Robson shot was off target as, predictably, Carlisle slowed down the action in the final ten minutes. Carlisle's Murphy got back to deny Forte as he looked to get on the end of McMahon's pass, whilst United's Murphy could not get enough on a header to trouble Gillespie.
Five added minutes gave the Blades hope but Forte fired over and the late aerial pressure failed to produce the coveted winner, even though Collins won the last header of the game.
Blades: Long, Maguire, Hill (Higginbotham 45), Doyle, McDonald, Kitson (Ironside 63), Collins, Forte, Robson, Poleon (J. Murphy 45), McMahon.
Unused: Westlake, Porter, McFadzean, Coyne.
Carlisle: Gillespie, Simek, McGovern (Manset 83), Livesey, Welsh (P. Murphy 77), Noble, Thirlwell, Miller, Berrett, Mustoe, O'Hanlon.
Unused: Collin, Loy, Cadamarteri, Potts, Beck.