The win moves the Iron five points clear of the League One relegation places.
Akpo Sodje opened the scoring as United flew out of the blocks in a fantastic first half performance. He headed his third in Iron colours after a Mark Duffy's inch perfect cross.
Three minutes later Paul Reid made it two. Tom Newey, who put in another excellent shift at right back battled to win a corner and Reid powered home a header when Duffy whipped it in.
Sam Slocombe allowed James Barrett's long-range effort to squirm under him just before the break to give Carlisle hope, before Sodje saw an effort rebound off the woodwork.
Jimmy Ryan went close just after the break, and deep into injury time Sodje sealed the three points to the delight of a boisterous Glanford Park with a clever finish after great work from Karl Hawley.