Dean Cox fired home the winner in first-half stoppage time as Orient overcame Coventry City – but it was not enough to keep their play-off dream alive.
With Swindon beating Stevenage it meant that Russell Slade’s side finished the game four points adrift of a top-six place, with just next week’s home encounter with Oldham Athletic to come.
But this was a brave performance by an injury-hit Orient team who impressed during the first half and weathered Coventry’s early second-half storm to emerge triumphant.
The O’s boss made just one change to the side that had beaten MK Dons, with Lee Cook returning from injury in place of Charlie MacDonald.
Indeed, so threadbare was the Orient squad, that the manager could only name four substitutes, including Lee Butcher.
Early exchanges at the impressive Ricoh Arena were even, but it was Orient keeper Jamie Jones who was called into action first as he made a regulation save from John Fleck and then acrobatically denied Jordan Stewart from distance.
But O’s soon settled and looked comfortable for much of the first half as Dean Cox revelled in a free role alongside 16-goal striker Kevin Lisbie.
Although Orient had plenty of possession they failed to create too many clear-cut openings and Coventry almost made them pay on 26 minutes when Steven Jennings threaded a ball through to John Fleck, but Jones parried his effort and skipper Nathan Clarke cleared off the line as Danny Philliskirk tried to fire the loose ball home.
As Orient continued to catch the eye they could so easily have taken a 28th-minute lead when Cook played in a delightful free-kick from the left and Jimmy Smith sent a header inches the wrong side of the post from close range.
Following a rash of bookings, Coventry wasted a good chance when Cyrus Christie blazed over after robbing Gary Sawyer. But with the game drifting into stoppage time Orient grabbed the lead their first-half performance just about warranted.
Moses Odubajo was the architect with a powerful run down the right and he cut in before rolling the ball into the path of Cox, who curled a shot across Coventry keeper Joe Murphy and into the bottom corner of the net.
Coventry made a change at the interval and brought on Jordan Clarke, but he quickly became the fourth home player to be booked for a foul on Lisbie and Martin Rowlands fired the resultant free-kick just wide.
The home side started to press and as O’s were forced onto the back foot David Bell headed an effort over just before the hour.
Then, Bell went close twice more in a three-minute spell both times catching out Leon McSweeney, down the left, but each time he failed to find a finish when well placed.
Sandwiched between those two efforts O’s almost added a second when another Rowlands effort flew wide of the mark following good approach play by Cox and Cook.
As the second half evolved Orient dug deep and regained a semblance of control as Coventry were reduced to long-range efforts with Franck Moussa going desperately close with a shot from 25 yards on 85 minutes.
But the O’s looked dangerous on the break and Lisbie and substitute Lloyd James both had chances to wrap the game up.
However, in the end it mattered not, as Orient comfortably survived three minutes of stoppage time to record their 21st win of the season, much to the delight of the 893 travelling fans, who were long gone before the Coventry players returned for a lap of honour.
Coventry City: Murphy; Christie, Martin, Wood, Stewart (Clarke 46 mins); Baker, Moussa, Jennings (Wilson 77 mins), Fleck, Bell; Philliskirk (McDonald 72 mins). Subs: Dunn, Thomas, McSheffrey, Edjenguele.
Coventry bookings: Wood (23 mins foul), Martin (36 mins foul), Christie (38 mins foul), Clarke (50 mins foul)
Leyton Orient: Jones; McSweeney, Clarke, Vincelot, Sawyer; Odubajo, Smith, Rowlands, Cook (James 85 mins); Cox, Lisbie. Subs: Butcher, Lee, Vanderhyde.
Orient goals: Cox (45+1)
Orient bookings: Rowlands (40 mins foul), Clarke (77mins handball)
Attendance: 11,234 (inc 893 Orient fans)
Referee: E Ilderton