Cheltenham Town's unbeaten run ends
The result all but confirms relegation for Martin Allen's team, who have six matches left before their three-season adventure in League One comes to an end.
The Robins trailed at half-time to Dean Morgan's 25th minute strike and slipped to their first home defeat since February 28, when they went down by the same scoreline to Northampton Town.
During an uneventful half, Orient made the breakthrough when Morgan latched onto a flick from Scott McGleish and placed a fine shot inside the bottom right corner.
Cheltenham went into the game unchanged, with Michail Antonio and Yuri Berchiche handed their home debuts.
Berchiche's Spurs team mate David Hutton started on the bench again.
It was only the third time Allen had kept his team the same in 40 matches since taking over last September.
Senior players John Finnigan and Shane Duff returned to the bench after injuries. Former Robins winger JJ Melligan started on the bench for Orient.
Former Orient man Paul Connor saw an effort deflected wide early on before Andy Gallinagh also tried his luck, but was off target.
Andy Lindegaard made a fine challenge to deny Orient a shooting chance, but there was a real lack of goalscoring opportunities.
Connor saw a header blocked from Frankie Artus' cross with the outside of his left boot.
A training ground free-kick routine ended with Michael Townsend's shot rolling wide shortly before Orient took the lead.
Elvis Hammond was booked in the 27th minute for kicking the ball away after being caught in an offside position.
Hutton and Marley Watkins were brought on for the start of the second period in place of Michail Antonio and the ineffective Leon Constantine.
Connor was sent up front after starting on the left wing and he powered a shot over the bar in the 46th minute.
Only some heroic defending from Townsend prevented Orient from scoring a second in the 50th minute.
Morgan's ball found McGleish, who got the better of Lindegaard and the striker's low shot beat Brown, but Townsend blocked and then threw himself in front of Simon Church's follow-up attempt on the line.
Cheltenham showed signs of improvement in the second half, but Paul Terry's left foot chip had Brown leaping across his goal, but it was a yard too high in the 69th minute.
Connor set up Hutton for a chance in the 74th minute, but Jamie Jones in the Orient goal made a fine reflex save.
Watkins made several exciting runs, but was guilty of holding onto the ball for too long at times.
Melligan was introduced to the action with seven minutes to go, while Duff replaced Berchiche at left-back, who had picked up an injury on his home debut.
Cheltenham thought they they should have been awarded a penalty when Andy Gallinagh's cross appeared to have been handled by James Smith, but appeals were waved away with five minutes to play.
Melligan's first run ended with him being wrestled to the ground by Artus, but Charlie Daniels' free-kick was wasted for Orient.
Cheltenham forced a succession of corners during stoppage time and Brown was racing forward to add his height to the attack, but the flag kick was taken too quickly and he had to return to his goal.
CHELTENHAM TOWN: S Brown; A Lindegaard, D Diallo (c), M Townsend, Y Berchiche (S Duff 84); M Antonio (M Watkins 46), A Gallinagh, F Artus, P Connor; E Hammond, L Constantine (D Hutton 46). Subs: W Puddy, J Finnigan
LEYTON ORIENT: J Jones, S Purches (c) (A Thelwell 70), T Mkandawire, J Spencer, C Daniels; J Demetriou, P Terry, J Smith, D Morgan (W Gray 78); S Church (J Melligan 83), S McGleish. Subs: G Morris, B Saah.

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