Carlisle United 2 Leyton Orient 3: Ten-man Carlisle United's nine-game unbeaten league run was ended on a controversial afternoon at Brunton Park.
Goalscorer Ryan Edmondson was sent off in the first half as ref Thomas Parsons came in for criticism for a string of decisions.
Orient's Theo Archibald scored either side of Edmondson's United goal in the opening 16 minutes.
Aaron Drinan then put the visitors further ahead after the break, before Jordan Gibson gave Carlisle hope.
Paul Simpson's side pushed for an equaliser but their second defeat of the league campaign sent them down a place to seventh in League Two, as Orient went top.
It proved an eventful afternoon in front of a 5,590 crowd as the teams in sixth and second at the start of play went head to head.
Simpson welcomed fit-again Kristian Dennis and Fin Back into his starting line-up, Corey Whelan also passed fit to start despite a recent ankle injury, but a similar problem kept Jack Stretton out of the squad.
Tobi Sho-Silva was included among the subs for the first time this season on his return from a hamstring injury.
Visitors Orient recalled Idris El Mizouni as he returned from injury, with veteran Darren Pratley also coming into their side - and boss Richie Wellens making a change shortly before kick-off, Ruel Sotiriou stepping up from the bench to take Paul Smyth's place.
Carlisle made the worst possible start as they were caught cold inside the second minute, Archibald picking the ball up 30 yards from goal and running at the defence before shooting low past Tomas Holy.
United were quickly onto the front foot in response, with Dennis sending a looping header wide from an Owen Moxon free-kick.
Orient then almost made it two when Sotiriou found more space between Carlisle's midfield and defence, but shot wide.
Carlisle then levelled in the 15th minute when one of a string of corners was aimed in from the right by Callum Guy, and Edmondson found space to send a bullet header past keeper Lawrence Vigouroux.
It was his first league goal for the Cumbrians.
But parity only lasted a minute as Orient quickly regained their lead, a slip by Jon Mellish allowing Archibald to pick up the ball before sending a perfectly-weighted chip over a stranded Holy.
Carlisle had to respond again, and applied more pressure, but struggled to create any clear chances for a spell.
Mellish blocked an Archibald shot as Orient counter-attacked, before Moxon had to leave the field for stitches after a collision when defending a corner.
United were down to ten men for five minutes, after which it was decided Moxon could not continue, Jayden Harris taking his place in the 34th minute.
There were then two major flashpoints as, first, Carlisle were denied huge penalty shouts when a Guy cross struck Tom James' arm.
Soon afterwards, as players walked away from the Orient box, there was a clash between Edmondson and Pratley, the Os man going down and United's striker shown a straight red card for raising his hands to the visiting captain.
Edmondson now faces a three-game ban.
Simpson, having sent Mellish into midfield while Moxon was off the pitch, kept him there with Carlisle down to ten men for nearly two thirds of the game.
Archibald shot wide as he looked for a third while Carlisle applied pressure late in the first half, Gibson slicing wide and ref Parsons failing to spot some shirt-pulling on Dennis in the Orient box.
United's fans were further angered when Archibald went down cheaply in added time and stayed down, the two-goal Orient man booed as he eventually got to his feet.
The officials were then jeered down the tunnel at half-time with Pratley also coming in for United criticism.
Carlisle's hopes of a comeback were then dented by a third Orient goal five minutes into the second half.
As the visitors played the ball forward, Paul Huntington hesitated, awaiting an offside decision, but as Corey Whelan moved to try and interept the ball, the flag stayed down and Drinan - walking back from an offside position - pounced, racing away from the defender and finishing clinically across Holy.
Rob Hunt then shot wide from a good position for the visitors, with Carlisle initially struggling to get back into things, and then a sidefooted Tom James attempt went close.
But United then did halve the deficit with Gibson's first goal of the season.
The ten men did well to work a good attack down the right and when Back crossed low and Dennis dummied, Gibson was in space on the left of the box and fired it past Vigouroux.
And that set up a dramatic last half-hour which began when Back and Harris applied pressure on the right and Gibson saw a shot deflect wide.
Orient boss Wellens made two changes, bringing on Jordan Brown and Charlie Kelman, as sub Harris tried to drive United forward.
A sweeping move then saw Mellish and Gibson combine to feed Back, whose low goalbound shot was deflected behind.
Carlisle applied increased pressure, while ref Parsons had his cards out again as a Gibson challenge saw the Blues man booked, Mellish and Drinan also yellow-carded for the scuffling that resulted.
Another yellow was shown to Huntington for his furious reaction to another decision, as Kelman went down under a challenge, James' resulting free-kick held by Holy.
The Blues couldn't make the most of a free-kick of their own just outside the Os box as they continued to apply plenty of pressure in the visitors' half.
Mellish then saw a shot blocked on the edge of the box after a Back long throw was half-cleared.
Simpson then handed Sho-Silva his first outing of the season as a 78th-minute substitute for Dennis as Carlisle chased a late leveller.
Gibson chipped over the bar after Harris had won the ball back in Orient's half, and Guy sent a free-kick just over from the edge of the box.
United kept going, Sho-Silva and Back involved in a late attack which saw Gibson fire over in six added minutes and visiting keeper Vigouroux, who was often keen to delay taking goal-kicks and free-kicks, eventually booked for time-wasting.
The equaliser proved elusive, but Carlisle got a good reception from the home fans at full-time - Parsons and his fellow officials booed off again at the end.
United: Holy, Whelan, Huntington, Mellish, Back, Armer, Guy, Moxon (Harris 34), Gibson, Edmondson, Dennis (Sho-Silva 78). Not used: Kelly, Feeney, Charters, Ellis, Bollado.
Goals: Edmondson 15, Gibson 56.
Booked: Gibson, Mellish, Huntington. Harris. Sent off: Edmondson.
Orient: Vigouroux, Hunt, Beckles, Happe, James, Pratley (Clay 76), El Mizouni (Brown 61), Sotiriou, Moncur (Kelman 65), Archibald, Drinan. Not used: Sargeant, Ogie, Wareham.
Goals: Archibald 2, 16; Drinan 50.
Booked: Hunt, Drinan, Vigouroux.
Ref: Thomas Parsons.
Crowd: 5,590 (257 Orient fans).
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