United's run of midweek reserve games continued on Tuesday afternoon with a trip to Rockliffe Park to face Middlesbrough.
A mixture of youth and senior players came up against Boro's under-23 squad, which was suitably bolstered by the presence of first team players such as former-Blue Adam Clayton, Paddy McNair, Marcus Tavernier, Rajiv van La Parra, Jordan Hugill and Rudy Gestede.
The hosts started what was an overall very entertaining game brightly and Gray had to deal with an early chance as Gestede found space inside the area. A stinging shot was met by a firm parry.
United used the ball well but they were almost caught out when a delivery into the box took a ricochet before pinging around dangerously. A combination of a strong hand from Gray, the post and the crossbar denied the hosts the opening goal of the day as they tried frantically to slot it away.
Carlisle settled, with Thomas and McCarron looking to get forward from the flanks, and Thomas had the back line stretched when he weaved his way past challenges from wide. He connected well with his shot, but it angled wide of the upright.
Thomas was close again when he took charge of a free kick, after McCarron had been upended 23-yards out, but his curler whipped just past the angle of post and bar.
But it was Boro who asserted some authority when they won possession just inside the visiting half. Midfielder Adam Clayton shouted for it and he took a touch before sweeping an unstoppable shot into the bottom corner.
A precise through ball from Kennedy took McCarron into a good area but he blazed a shot over from distance as he tried to go for glory. And Thomas did the same as he bent his run from the left wing before chipping it just over the target.
It was a good spell for the Blues and excellent link up play between Brockbank and Thomas brought a fizzed delivery which caught the defence flat-footed. McCarron put his laces through it, and he was disappointed to see the ball crash down to safety off the underside of the bar.
United were made to pay for their misses just before the break when Boro once again nicked possession in a dangerous position. The dangerous Paddy McNair kept his eye on it and he crunched a rasper past Gray to double the advantage.
Both teams tightened things up in the second half, but Thomas thought he'd found a way through when he beat his man before steaming forward towards the box. The keeper somehow got there to make a fine one-handed save as a thunderbolt dipped towards his top corner.
That sparked another strong Carlisle spell and Simpson shielded a ball forward before spinning his man and going for goal from a tight angle. The keeper watched on in relief as it spun past his post.
A fantastic free kick delivery from deep from Glendon deserved better as it dropped inside the six-yard box. Kerr had a volley cleared off the line and Simpson tried to connect with the rebound, but determined defending preserved the clean sheet.
And Carlisle were dealt a late sucker punch when a huge ball forward was touched into the path of under-23 striker Mitchell Curry. He made no mistake as he dealt the visitors a real killer blow.
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Carlisle United - Gray, Barnes, Branthwaite, Grant, Brockbank (Birch 88), Kennedy, Casson (Galloway 70), Glendon, McCarron (Kerr 46), Simpson, Thomas (Charters 70). Subs - Ward, Lightfoot.