Leyton Orient 2 Carlisle United 3: George Tanner hit a last-minute winner as Carlisle United twice came from behind to win an eventful game at Leyton Orient.
The full-back got the decisive goal in a game which saw only one of three penalties converted and the Cumbrians also hit the woodwork twice.
Orient led early through Conor Wilkinson before the Blues' Offrande Zanzala saw a weak penalty saved.
Kemp was then denied from the spot by Magnus Norman at the other end, before sub Jon Mellish - on for the injured Zanzala - then fired United level.
Dan Kemp restored the Os' lead on the stroke of half-time but Carlisle fought back again with Lewis Alessandra making it 2-2 with the game's third penalty early in the second half.
Tanner then popped up to net his third of the season as United ended their final away game of 2020/21 with victory, leaving them 10th in the table and their unlikely play-off hopes now mathematically over, as they are five points adrift of the top seven with one game to play.
Blues boss Chris Beech resisted the temptation to experiment greatly with his side, making only two changes in east London.
That saw Alessandra and Omari Patrick come in for Mellish and the injured Rhys Bennett.
Beech decided against handing chances to the likes of Cedwyn Scott, Taylor Charters and Ethan Walker, preferring to go with his senior outfield men - while Norman kept his place in goal.
Orient boss Jobi McAnuff brought himself back into the side amid four changes.
And his side took an early lead when United skipper Nick Anderton allowed a ball forward to bounce, enabling Wilkinson to get behind him and stroke a low shot past Norman.
United tried to fight back from that third-minute blow but almost went two behind on 14 minutes when James Brophy squared for Wilkinson, who should have scored - but was denied by Anderton on the line.
Carlisle then had a golden chance to level when Zanzala was brought down by Dan Happe in the box.
But the striker's weak penalty was easily saved by home keeper Lawrence Vigouroux.
Zanzala lasted little longer as a hamstring injury forced him off after 22 minutes, Mellish taking his place.
And just two minutes later it was Orient's turn to blow a chance from the spot.
Ref Sam Allison penalised Norman as he brought down Wilkinson when the frontman had again got behind the Blues defence.
But the keeper atoned by diving to his left to push away Kemp's penalty.
An eventful first half saw McAnuff slice a shot wide and Joe Riley fire over the bar for the Blues.
Carlisle then did level when Aaron Hayden and Joshua Kayode kept a Callum Guy corner alive, and Mellish arrived to sweep the ball past Vigouroux.
Omari Patrick saw another effort saved before more sloppy defending cost United in first-half injury time.
Hayden was the culprit this time, his weak backpass allowing Kemp to pounce, go around Norman and drill the ball into the unguarded net on 45 minutes.
Carlisle could have levelled in first-half added time when the ball broke to Joshua Kayode, but his low shot past Vigouroux came back off the post.
United hit the woodwork a second time after the break when Joe Riley's 51st-minute shot hit the top of the crossbar.
But they did level three minutes later when Alessandra was brought down by McAnuff, and Allison pointed to the spot a third time.
Alessandra took it himself and his low shot went in off the left-hand post.
Both sides made substitutions in search of a winner, Beech bringing on Ethan Walker, while Norman made a good save to deny Wilkinson with a near-post shot.
At the other end, Walker failed to get his shot on target after Hayden had laid a Kayode long throw into his path.
The Preston sub was later booked and was then substituted himself, as Beech opted to withdraw Walker - the forward possibly struggling with an injury - and send on Scott for the final four minutes.
Orient almost won it at the death but sub Danny Johnson couldn't convert a cross from the dangerous Brophy.
But United then went up the other end and did snatch a third when Tanner won the ball in the Blues' half and drove forward, Alessandra attacked down the right and Tanner arrived on the edge of the box to drill a low left-footed shot into the bottom corner for his third of the season, and a first win in seven for the Cumbrians.
Carlisle are now highly likely to finish the season in 10th place, with 11th-placed Orient four points behind them, and ninth-placed Salford three points ahead with a much superior goal difference.
Leyton Orient: Vigouroux, Widdowson, Cisse, Happe, McAnuff (Clay 63), Wilkinson, Kemp, Brophy, Dennis (Johnson 63), Akinola, Turley (Ling 46). Not used: Sargeant, Sotiriou, Freeman, Abrahams.
Goals: Wilkinson 3, Kemp 45
Booked: Happe, Clay.
United: Norman, Tanner, Armer, Anderton, Hayden, Guy, Riley, Alessandra, Patrick (Walker 63, Scott 86), Zanzala (Mellish 22), Kayode. Not used: Farman, Devine, Charters, Dixon.
Goals: Mellish 42, Alessandra 54pen, Tanner 90
Booked: Walker, Mellish.
Ref: Sam Allison.
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