Highflying Mansfield climbed to second spot, consigning Carlisle to a club record ninth league defeat in a row.
Ex-United striker Junior Mendes proved a constant threat and his dazzling solo effort added to his assist Wayne Corden's opener.
Mansfield started brightly with Mendes crashing his close-range shot against the bar and Tom Curtis sending his drive just wide of Matt Glennon's post.
But Carlisle fought back and in the 21st minute Paul Arnison was unlucky to see his 30-yard drive tipped onto the bar by the scrambling Kevin Pilkington.
The visitors continued to dominate and it was no surprise when Corden gave them the lead in the 54th minute.
Mendes was allowed to turn in the box and float a cross to Colin Larkin, whose header rebounded off the bar only to fall to Corden, who volleyed past Glennon.
Nine minutes later, Mansfield added a second when Mendes made up for his early miss with a great individual strike.
Picking up the ball near the corner flag the powerhouse striker jinked past Arnison and shielded the ball from Lee Andrews before finding space for a low drive from the edge of the area, which nestled into the bottom corner.
Carlisle sent on Brian Wake and Adam Rundle in an attempt to kick-start a fightback, but the closest they came was Kevin Henderson's diving header, which flicked off the top of the bar.
United boss Paul Simpson admitted: "The second half was dire. We matched them in the first half, but then went out and waited for something to go against us." Stags manager Keith Curle said he always felt his side would eventually score.
"Carlisle stopped us from playing in the first half, but we knew we'd create chances if we carried on for 90 minutes," he said.