Wrexham tightened their hold on the third automatic promotion spot and plunged United deeper into relegation trouble.
Leading scorer Andy Morrell bagged a hat-trick, taking his total to 33 League goals for the season, a new post-war record for the Welsh club.
Wrexham were far too fast for United but they had a couple of early escapes before keeper Matt Glennon brought Lee Trundle down for Andy Morrell to open his scoring from the spot.
Morrell added his second ten minutes later slicing the ball inside the post after Stephen Roberts had failed in trying to turn Darren Ferguson's corner in from close range.
Brian Carey scored the third, again from a Ferguson corner and finished with a header inside the right post to put the home side well in control at half time.
Carey added the fourth soon after the break, this time Ferguson setting him up with a low free-kick into the box.
With a four-goal cushion, Wrexham took their foot off the gas and it was no surprise when Brian Wake grabbed a goal for United, heading home from a Ryan Baldacchino cross.
The Carlisle goal unsettled Wrexham for a while and they had a dodgy spell before Morrell headed in from a Shaun Holmes free-kick to complete his hat-trick and Carlos Edwards wrapped it up, beating keeper Glennon with a low shot from 30 yards.
Wrexham manager Denis Smith said: "We did not play brilliantly but none of our players had a bad game. We want one win from our three remaining matches to go up so it would be nice to do it in front of our home crowd on Saturday." Disappointed Carlisle manager Roddy Collins said: "It was always going to be difficult for us here. We had one or two chances before they scored and if we could have knocked one in it might have made a difference.
"We were booed off by our own fans and laughed at by Wrexham supporters, but we are not out of it yet."