PINT-SIZED striker Peter Duffield made an instant impact as Carlisle put the brakes on Town's Third Division promotion push.
Charlton goalkeeper Paul Rachubka hasn't done much wrong since joining Town on loan last week.
But his first mistake proved costly as Duffield, brought in on loan from Boston only yesterday morning, pounced for a 72nd-minute winner.
Distracted by hard-working home midfielder Brendan McGill, Rachubka and wing-back Anthony Lloyd got in a terrible tangle as they tried to deal with Andy Preece's driven low cross from the left at the near post.
The ball squirted into the six-yard box and Duffield was left to sidefoot home.
It was a goal which gave Carlisle fresh impetus in their desperate battle to avoid relegation from the Nationwide League and prevented Town from going third at the expense of Oxford, the team they beat so convincingly on Saturday.
A Town win would have put them second, and while it might have happened but for goalkeeper Matt Glennon, who twicd made vital saves from Andy Booth, it would have been unfair on a Carlisle side featuring three ex-McAlpine men in Chris Billy, Kevin Gray and Tom Cowan.
Brunton Park has never been a happy hunting ground for Town, who had lost on their three previous visits and won only three of 19 games at the Cumbrian outpost going into last night's contest.
And they got what they deserved on this occasion, because the passion and desire which fuelled Saturday's victory at the Kassam Stadium seemed to have been lost somewhere on the M6.
There was also a lack of direction, and it was disappointing that after going behind, Town failed to put any sustained pressure on an increasingly nervy home side.
Even when they were handed set-piece opportunities late on, Carlisle were let off the hook, with Andy Holdsworth's free-kick and Nathan Clarke's long throw being cleared without a penalty-area challenge by a visiting player.
And Carlisle old boy Tony Carss shot high and wide from a free-kick taken 10 yards forward by Tyne and Wear referee Colin Webster after a show of dissent by Preece, the former Bury player-manager.
Town, in fact, managed only two genuine efforts on target in the whole game, both falling to Booth, who enjoyed a rare old tussle with his former teammate Gray.
The first arrived in the 11th minute, when the striker met Carss' cross on the turn to fired in a neat left-foot shot which Glennon did well to tip for a corner.
The second came seven minutes into the second half, when Pawel Abbott's persistence set up raiding right-back Holdsworth for a low cross from which Booth's shot was smothered.
Midfielder Jon Worthington, making his 50th League appearance, was eager to shoot early on but sent one effort wide and the other well over.
Meanwhile Abbott had penalty claims turned down after he tumbled in a double Carlisle challenge when cutting into the penalty area after being set up by Carss in the 15th minute.
While Town might have had cause for complaint on that occasion, they had a let-off in the 33rd minute, when centre-back Efe Sodje clearly handled in the box, but Webster decided he had been fouled by Craig Farrell.
Earlier, Farrell was frustrated when Rachubka parried his low 15th-minute shot, while six minutes after that, Town had a big let-off when from a free-kick conceded by Sodje, Billy pumped the ball in, Preece nodded it down and midfielder Will McDonagh, who had both time and space, fired his shot high over the bar.
Preece wasted a 28th-minute free-kick when he fired the ball straight into the Town wall, while two minutes later, Farrell was unlucky when after dispossessing Lloyd and charging down the Carlisle right, his low angled shot flashed across the face of goal and just wide of the far post.
While Town were forced to replace injury victim Steve Yates with David Mirfin two minutes before the break, the back five still looked reasonably settled, although Duffield did manage to find space for a 58th-minute header from McGill's cross which he directed straight at Rachubka.
When, six minutes later, Duffield's glanced header from Cowan's cross flashed inches wide, it looked as if his luck was going to be out.
But the debutant was to get his golden chance, leaving Town to contemplate a below-par performance and the need for a major improvement when Macclesfield, another side battling for League survival, visit the McAlpine on Saturday.
How they rated:
Paul Rachubka Will be more than disappointed not to have kept a second clean sheet in as many Town appearances. Rating: 6/10
Andy Holdsworth Worked hard in defence and never stopped trying to provide service from the right but not one of his best displays. Rating: 7/10
Anthony Lloyd Made a nervy start and struggled to cope with the runs of surging midfielder Brendan McGill, but tried hard. Rating: 6/10
Steve Yates Looked solid and dependable until a hamstring injury forced him off just before the half-time break. Rating: 7/10
Efe Sodje Not quite as marvellous a performance as that produced down at Oxford, but not that bad either. Rating: 7/10
Nathan Clarke Another impressive display, and it's a pity his teammates couldn't make better use of those long throws. Rating: 7/10
Tony Carss Not at his best on return to one of his old stomping grounds. Wasted a late free-kick opportunity. Rating: 6/10
Jon Worthington Never shirked a challenge, but like too many of his colleagues, not one of better performances. Rating: 6/10
Danny Schofield Had a quiet game and struggled to make any real impact in the face of some crunching Carlisle tackling. Rating: 6/10
Andy Booth Felt the force of Kevin Gray's boot on more than one occasion, and unlucky to be denied with early effort. Rating: 7/10
Pawel Abbott Failed to score for the second match running, but it wasn't for the want of trying. Showed some classy touches. Rating: 7/10
Focus on: Pawel Abbott >>>
Focus on: Pawel Abbott
He might have been unable to find the net, but the loan man from Preston still showed he has plenty to offer Town as they push for automatic promotion. Had a solid penalty appeal turned down when crunched by Tom Cowan and Kevin Gray.
Clearly that 72nd-minute moment when Carlisle's loan striker Peter Duffield, who played for Boston against Town earlier this year, beat Rachubka, left, to turn an average night for Peter Jackson and his side into a bad one.
Town subs used: Mirfin (for Yates, 43mins), Newby (for Schofield, 74mins).
Town subs not used: Edwards, Fowler, Senior..
Scorers: Carlisle: Duffield 72mins.
Referee: Colin Webster (Tyne and Wear).
Bookings: Carlisle: McDonagh (foul), Preece (dissent). Town: Abbott (foul).
Corners: Carlisle 3, Town 2.
Caught offside: Carlisle 2, Town 1.
Free-kicks awarded: Carlisle 20, Town 17.