Both sides created chances on a wet, wintry afternoon at Brunton Park but it was United who took the win courtesy of goals either side of the break from Richie Bennett and Samir Nabi.
Fleetwood started the game positively and Bacon was the first of the keepers to be called into action when a good break left room for a shot. The home stopper went low to parry it away and O'Sullivan stepped in to complete the clearance.
The visitors enjoyed a lot of early possession, without managing to find a way through, and United started to settle as they found their passes and used the ball better through the middle areas of the pitch.
A good move down the left flank saw McCarron use Egan as a bounce board and Bennett pulled off his man to make room for a shot as he called for the pass. He caught it cleanly but it was too close to the keeper.
More good Carlisle play followed and O'Sullivan was disappointed when he lost his bearings having got on to the end of a good move. He connected with power but it was always going wide.
The Cumbrians took the lead when Richie Bennett looked up just as the ball fell nicely in front of him 35-yards from goal. He spotted the keeper off his line and made no mistake with an excellently executed lob.
The away side immediately looked for an equaliser and Bacon had to go full length to tip a stinging drive round his post as the ball flew through a ruck of bodies.
The Blues countered from the corner and both Hope and Bennett were unlucky as they beat the stranded keeper with goal bound efforts. Strong defending on the line twice denied the striking pair.
The second half was end-to-end and midfielder Samir Nabi wasn't too far away when he tried to guide a first-time shot into the top corner from the edge of the area. It bent and dipped but dropped just over the target.
Fleetwood enjoyed a good attacking spell, and Bacon went low to make a great block as it looked like an equaliser was on the cards.
The red shirts stayed forward and the Fleetwood bench looked on in disbelief as two stabbed follow-up shots both smashed back off the woodwork.
Carlisle made the visitors pay for their misses when Samir Nabi took charge of a free kick on the left hand angle of the penalty area. His delivery whipped past everyone and found its way into the back of the net via the inside of the post.
Egan and Ellis had chances from set pieces to extend the United lead further, but Fleetwood threw men forward as they looked to get something out of the game with the clock ticking down.
Crosses and deliveries zipped across the face of goal, and the consolation finally came when a deep corner was met by two players at the back stick. It seemed to take an age before it was eventually bundled over the line.
United - Bacon (Ashton 80), Egan (A Trialist 46), Miller (Salkeld 75), Ellis, Olsen, McCarron (Egan 65), Etuhu (B Trialist 60), Nabi, O'Sullivan (McCarron 80), Hope (Hutchinson 60), Bennett (Dixon 60).
Goals - Bennett (27), Nabi (60)
