Heavy rain meant a heavy surface at the Matchroom Stadium but an agreement from both clubs to get the game on meant it was kick off as planned on what became a very sticky surface.
It looked to be an evenly matched affair until an enforced early substitution for the away side handed the initiative to an in-form team who proceeded to press home their advantage.
And Carlisle United were left with plenty to discuss as a harsh sending off and some haphazard defending combined to add to their downfall.
“We come away from this feeling very, very disappointed," Greg Abbott said. “Big decisions have gone against us and that has left us feeling very sorry for ourselves. They are a side on a good run and they got their tails up, and we're obviously not happy about some of our defending at all. It's been a bad day but we will get ourselves together and make sure we come back from this.”
A deep corner from Cox found Clarke unmarked as the O’s started at pace and he had time to make his leap as the defence stood static. Gillespie stepped across to push the goal-bound effort behind.
A direct run from the dangerous Kevin Lisbie took him past Simek and Cox called for it as he arrived late on the edge of the box. His touch opened a gap but a weak shot was easily gathered by the Carlisle stopper.
The Cumbrians worked hard to get into the game and a blocked drive from Berrett following some good build up play fell nicely for teenager Brad Potts in the middle of the park. He let fly from 28 yards but Jones did enough to readjust and tip it over the bar.
Justice was done for Carlisle on 13 minutes when they found themselves on the wrong end of a dubious handball decision when Gillespie was judged to have picked a sliced Livesey clearance off the floor just outside his area. Nathan Clarke went for power but Berrett made a block to draw a line under what would have become a major talking point had it led to a goal.
The visitors almost grabbed the lead when they won a free kick on the right hand touchline. Nathan Clarke got the top of his head to the Mustoe delivery and he was relieved to see it bounce back off the upright. The rebound bobbled frustratingly through O’Hanlon’s legs as he raced forward and Vincelot stood tall to block a thundering volley from Robson.
The first half started to fall apart for United just after the half hour when influential centre back Danny Livesey signalled to the bench following a stretch for a ball inside his own area. Orient sensed a hint of hesitation and a string of crosses followed as they tested the back line. Romain Vincelot made the deliveries count when he nipped between two green shirts to power a header home.
Lisbie should have done better to convert a Cook inswinger as the O’s increased in confidence and both Cox and Odubajo wasted good chances to double the lead as a mishit shot was followed by a wild slice into the stands.
With half time just seconds away the lead was doubled as the Cumbrians got themselves into a real mix at the back. Cox and Lisbie seemed to be everywhere as they tried to force it through and it was left to Cook to put it on a plate for Shaun Batt, who had held his position inside the six yard box. A touch from the inside of the boot was enough to leave Gillespie flapping at thin air.
The second half took a while to get going but the game should have been wrapped up on the hour when Shaun Batt moved into space. His pass released Dean Cox but the nippy wide man choked as he scuffed a weak shot right at Gillespie.
United started to see more of the ball and a cross from Mustoe had Beck interested as he leaned into his man. He got there but he could only glance his header wide of the target. That was followed up by a flowing move when Berrett carried the ball forward. He found Beck, with his back to goal, and a neat lay-off brought a thundering drive from Thirlwell. Mark Beck tried to make something of the block but he slipped a she tried to shoot and the save was easy for Jones to make.
The introduction of livewire Charlie MacDonald caused immediate problems as he was played through. He touched the ball round the advancing Mark Gillespie and the keeper was left with his head in his hands as he was shown his second yellow card of the day. Kevin Lisbie placed the ball on the spot and he did the honours with a perfectly placed spot kick.
Substitute Dave Symington brought a diving save from Jones as he tried to find the bottom corner with a crunching free kick. Winger Matt Robson gave the large travelling contingent something to cheer, when he rattled his eighth of the season into the back of the net via the inside of the post when he surged through on the left.
Orient finished the game on top as they used their man advantage and David Mooney rattled the woodwork as he clipped a shot underneath Collin. The big Carlisle keeper then produced a superb save to deny Lee Cook as he tried to force one in at the near post.
But the day belonged to the O's and Dean Cox sealed the deal with a last minute strike as he kept his cool from the edge of the 18-yard box.
Leyton Orient - Vincelot (33), Batt (45), Lisbie (69 pen), Cox (89)
Carlisle United - Robson (78)
Leyton Orient - Clarke (73)
Carlisle United - Gillespie (13 & 67 - sent off), Murphy (33)
Leyton Orient - Jones, McSweeney, Vincelot, Cuthbert, Cox, Lisbie (Mooney 72), Clarke, Odubajo, Cook, Rowlands, Batt (MacDonald 67). Subs - Sawyer, Smith, Grainger, Omozusi.
Carlisle United - Gillespie, Simek, Livesey (Murphy 29), O'Hanlon, Mustoe, Potts, Thirlwell, Berrett (Collin 68), McGovern (Symington 59), Beck, Robson. Subs - Welsh, Noble, Loy, Cadamarteri.
Referee - Mr Simon Hooper
Attendance - 4,387 (431 away fans)