United's final Central League Cup group game was away to Morecambe on Thursday afternoon.
The Blues went into it with one win and one defeat under their belts - against Fleetwood and Preston respectively - and knowing that they needed a victory to make it through to the area semi-final.
First-team squad members Gime Toure and Josh Dixon were given another opportunity to get some valuable pitch time, with the remainder of the team made up of youth first and second year players.
The first chance of the day went to the Blues as Bollado fed Toure with a decent ball. A touch was followed by a shot from distance but it bounced just wide of the upright.
An excellent through ball from Watt released Toure once again moments later, and he jinked his way past a challenge before letting fly from 12-yards. The keeper dived low to tip it round the upright.
The Shrimps got forward with purpose on nine minutes as they edged their way through the middle of the park. It opened up and an effort from range had to be gathered by Simons.
There was a superb save from the Morecambe stopper when Watt beat the offside trap to go clean through. He had just one thing on his mind as he unleashed a thunderbolt, but the keeper showed strong hands to beat it away.
Watt rifled another fierce rocket wide from the edge of the area as the Blues dictated the pace, but the Shrimps sent a reminder that it wasn't going to be an easy afternoon with a cross from the right flank which flashed untouched across the face of the target.
A huge ball over the top caused problems for the reds when Bollado used his strength to put pressure on the back line. He got the slightest of touches but the stopper was alert and he got a boot to it to prevent it from going over the line.
Morecambe went close when unexpected space brought a pilderiver from 22-yards, but it was always heading high and Simons was able to watch as it sailed into the ether.
Half chances came and went for United, with Dixon and Toure both having a go, and it was the Blues who ended the first period on the front-foot when Fishburn and Toure exchanged passes inside the box. The latter tried to finish the move off but his volley lacked power.
The hosts came out of the dressing room fired up and a cheeky back heel from a corner that had been nodded back into the mix dropped just over the Carlisle crossbar.
A run from Toure took him past two, but a low punt was straight at the keeper as United tried to get themselves going.
And the Shrimps claimed the lead on 54 minutes when a ball over the top was taken under control inside the area. A ripping volley from a tight angle bulged the inside of the net as Simons tried to get there.
There was real concern for the Cumbrians when midfielder Josh Dixon went down with a loud scream just before the hour mark, and he was replaced hy Mason Hardy as his treatment continued by the side of the pitch. He was eventually taken down the tunnel looking visibly upset.
Carlisle pulled level on 70 minutes when Kilsby ghosted into the box. His crunching attempt was parried, but Watt was there to follow up after Toure had kept it alive. He beat the keeper, but not the post, but Fishburn was there to guide it into the waiting net.
The Blues were suddenly rejuvenated and Kilsby blazed over from close range when he found himself unmarked as he arrived at the far post to meet a deep delivery.
But Simons needed to be at his best when red shirts flooded forward. A fizzed strike was top corner bound until the agile keeper went full length to claw it away.
Carlisle took the lead in style with 13 minutes left to play when Toure bent a run into the area from the right flank. His connection was clean, and the keeper could only watch in anguish as it came off his gloves and pinged into the corner of the net.
Substitute Mason Hardy sent a clip on the run just wide as the clock ticked down, and Fishburn had a volley blocked at source as he looked to finish the game off.
Watt was next to show when he ran at the heart of the back line with the ball at his feet. He left two in his wake but more good work from the keeper thwarted the strike.
The Morecambe glovesman was excellent yet again late in the day when he somehow got to a Fishburn grasscutter that looked to be a certain goal. A firm hand got there to scoop it away.
United saw the game out and it's on to Preston North End in the competition's semi-final.
United - Simons, Potts, Carr, Gordon, Kilsby, Dixon (Hardy 64), Watt, Bollado, Taylor (Hill 71), Fishburn, Toure. Subs - Boyd (gk), Ellis.
Goals - Fishburn (70), Toure (77)
Referee - Nik Storey
Assistant Referee 1 - David Gillon
Assistant Referee 2 - Callum Black
