Orient's slim hopes of automatic promotion were extinguished at Crawley after they slipped to a 2-1 defeat in Sussex.
Brentford's win over Preston and Wolves' defeat of Rotherham means the Bees have an insurmountable 10 point lead over the O's with three games to play.
The O’s fell behind against the run of play when debutant Gwion Edwards opened the scoring for the home side before Chris Dagnall levelled it when he prodded home a Mathieu Baudry knock-down from a corner.
Edwards starred for the home side in the second period but a goal from Andy Drury was enough to seal it as Orient failed to grab another.
There were two changes for the O’s from the side that demolished Gillingham as John Lundstram dropped to the bench with Lloyd James replacing him and Chris Dagnall partnering David Mooney in attack with Kevin Lisbie making way.
Orient were intent on breaking the curse of Crawley, having never taken a point from their opponents in their previous encounters.
It was a scrappy start with the only half opportunity coming from a Mathieu Baudry punt that almost allowed Dagnall in after defensive hesitation from Kyle McFadzean whilst Mike Jones forced Jamie Jones into an early save from distance.
The opening 10 minutes didn’t see much of the free-flowing football that characterised the O’s win against Gillingham but with a dozen minutes gone Orient produced the first move of class as they worked it left to Dagnall who pulled the ball back into the path of Elliot Omozusi who was a whisker away from his first career goal when he bent an effort narrowly over on the angle.
Moses Odubajo started to find room to open his legs and began to play more of a prominent role as the O’s won their first corner with a quarter of the game gone. James fired in a low corner that Romain Vincelot headed well towards goal only for Paul Jones to save, whilst a minute later Dean Cox went close with a whipped shot from the right as Orient established control.
It was the home side though that grabbed the lead against the run of play when Dannie Bulman cut the ball across the face of goal from the right hand side that allowed debutant Gwion Edwards to slot home from 12 yards.
The O’s would have been disappointed with the space allowed to the Crawley forwards but the goal seemed to galvanise the O’s in the short term as within a minute Mooney went close from a Dagnall cross before the latter almost poked a through ball past Jones in the Crawley goal.
Dagnall had looked sharp and got his reward with one of his simpler goals of the season. James sent a corner in from the right that was headed down by Mathieu Baudry allowing the striker to poke home from close range to send the sides in level at the interval.
Orient were slightly slower out of the blocks for the second period than the home side as the goal scorer Edwards looked their biggest threat with his pace on the left and he went close with a bending shot eight minutes into the half.
The O’s looked sharp on the counter though and when Mooney led the charge just before the hour mark, he let fly with a shot from distance that had Paul Jones scampering across his goal but dropped wide.
Edwards still looked the danger man for the home side and he twice went close within a minute when first of all he stung the fingertips of Jones with an effort from distance before his header from an Andy Drury corner was cleared off the line by Odubajo.
Shaun Batt entered the fray in place of Dagnall whilst John Lundstram came on for James as Slade looked for a winner.
However Orient were made to pay again for some more loose defending as Drury found space at the back post to head a deep cross from Mike Jones back across goal and into the bottom corner.
Orient weren’t at their best but still had a glorious chance to level it again when a Cox free-kick fell kindly for Mooney inside the box but the leading scorer failed to make decent contact on a volley.
Meanwhile Edwards continued to run the show for the home side as he played in the skipper Josh Simpson but Jones got down well to deny him.
The O’s huffed and puffed in the final 10 mins as Mooney had an effort blocked on the line yet will have been disappointed not to have worked Paul Jones more as the curse of Crawley remains for the O’s.
Crawley: Jones, Sadler, Connolly, McFadzean, Drury, Simpson (C) (Torres 85), Walsh, Bulman, Tubbs(Proctor 60), Jones, Edwards
Subs: Essam, Fallon, Monakana, Maddison, Dicker
Goals: Edwards (25) Drury (70)
Orient: Jones, Omozusi, Vincelot (Ness 79), Cuthbert, Baudry, Cox, James (Lundstram 66), Mooney, Odubajo, Clarke (C), Dagnall (Batt 66)
Subs: Sawyer, Larkins, Lasimant, Simpson
Goals: Dagnall (39)
Referee: Mick Russell
Attendance: 4,387 (1171 away)