United's first away league game of the season was the long trip to Oxford on Saturday afternoon.
There were two changes to the team that started against Fleetwood last weekend with Taylor Charters into the midfield trio at the expense of Owen Moxon, who was suffering from an illness bug.
Ryan Edmondson was given the nod ahead of Luke Plange, following his outing up front with Jordan Gibson at Harrogate on Tuesday night.
There was a skirmish from the kick off for the Blues when Moore misjudged a clearing header. Charters and Armer worked the left wing, but it wouldn't quite sit right for either Back or Gibson to strike.
A surging run from the halfway line from Browne looked dangerous for the home team until Paul Huntington casually put a toe out to steal the ball just as the winger shaped to shoot.
Excellent work from Gibson a yard outside the box saw him keep things under his control despite having lost his footing. Guy lurked, and he was a whisker away with a thundering shot that angled across the face of the target.
It was a bright start from Gibson and he sent Mellish on an overlap with space to exploit. The cross was behind Edmondson and Negru swept it to safety.
More good visiting football came as Mellish nipped in to turn it over inside his own half. Off he went, and once again Gibson was an outlet. His cross skipped off the surface and Beadle gathered it in at the second attempt.
Oxford showed on 16 minutes when Bodin brought left back Brown into play. A fizzed delivery skimmed along the ground but Lavelle was there to hook it high before Harris could get a touch.
Lavelle was just as important moments later when Harris went for the heart of the back line. The defender stood tall before getting in the way with a much-needed block.
United were calm in defence once again on 25 minutes when a dipper of a free kick rifled towards the six-yard area. Huntington was precise with his touch.
Carlisle had a set piece at the other end when Guy was felled. Charters took charge of it, but he put too much on it and it bent harmlessly behind.
The hosts were incisive with a breakaway when Rodrigues put a pass through for Browne to go after. His low cross begged to be tapped home, but there was nobody there.
Harris looked to be offside when he was sent beyond the blue rearguard just past the half hour, but the flag stayed down. Mellish was excellent with a recovering scamper that terminated with a sliding tackle.
Mellish foiled Harris once more when the nippy front man dropped a shoulder to take on a pass from Rodrigues. His block was firm.
It was nip and tuck, with both sides causing problems, and a 22-yard ripper from Guy had to be stopped by Moore or it really would have been interesting.
The U's probed in the lead-up to the break, but Holy showed safe hands when Brannagan let fly from distance in time added on.
There was a let-off for the away team at the start of the second period when a wayward pass from Lavelle on the halfway line allowed Harris to bear down on goal. He hesitated at the vital moment, and that allowed the retreating defenders to recover.
A free kick from out wide from Brannagan brought a punch from Holy, but that was snaffled up on the edge of the area. Advancing blue shirts were needed to charge the volley from Rodrigues down.
The U's were having the better of it, and Bodin had his face in his hands as he curled wide from distance after a slick exchange of passes between Browne and Harris.
Carlisle were better on 61 minutes when Guy pulled into space. He clipped a lovely ball into the box but Edmondson's header was too close to Beadle to be of much concern.
Mellish was next to bring options as Gibson and Armer combined, but Negru got there before Back could steam in.
Substitute Stan Mills was a danger when he came on, and Lavelle had to go for safety from the first of the wide man's deliveries. The corner was well marshalled by Charters.
A scuffed clearance from Huntington was followed by a rushed tackle, as the hosts pounced, and that left a debate for the yellow shirts as to who would take the 22-yard set piece. Bodin wasn't too popular as he popped it high.
The home team took the lead from absolutely nowhere as a seemingly harmless ball over the top brought hesitation. Holy stood his ground and Mark Harris gave it the deftest of touches. That was enough to send it into the bottom corner as it evaded the dive from the big stopper.
Mellish tried to take matters into his own hands in response as he rode three tackles during a winding run from deep. He had Edmondson beside him, but the cross to the back stick was once again dealt with.
Oxford almost hit on the break again late in the day when a slip from Plange left Brannagan with options. Goodrham was alert, and he went for the far corner, only to send it wide.
Brannagan went for a snapshot that was straight at Holy as time ticked away, and up at the other end it was a succession of two corners for the Blues. Garner's shot was blocked for the first, with McCalmont suffering the same fate for the second.
One-touch passing almost unlocked the door as Carlisle kept going, but Harris looked on in exasperation as his ball into the six-yard box went untended.
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Goals
Oxford United - Harris (76)
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Bookings
Oxford United - Harris (39), O'Donkor (90+6)
Carlisle United - Guy (51), McCalmont (60), Back (62), Huntington (73), Mellish (90+6)
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Teams
Oxford United - Beadle, Long, Brown, Moore (c), McEachran, Brannagan, M Harris (O'Donkor (0+1), Bodin (Goodrham 75), Browne (Mills 67), Rodrigues (McGuane 75), Negru. Subs - Eastwood, Smyth, Stevens.
Carlisle United - Holy, Lavelle, Huntington (c) (Garner 80), Mellish, Back, McCalmont, Guy (J Harris 88), Charters, Armer, Gibson (Butterworth 70), Edmondson (Plange 80). Subs - Andresson, Whelan, Barclay.
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Match officials
Referee - Jeremy Simpson
Assistant Referee 1 - Johnathon Bickerdike
Assistant Referee 2 - James Vallance
Fourth Official - Stephen Parkinson
Observer - Ian Corner
Coach - Philip Gibbs
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Attendance - 7,964 (770)