Reading FC were on the end of a dismal home defeat against the side who started the day at the bottom of the League One table.
Young goalkeeper Coniah Boyce-Clarke had a game to forget as his blunder from Charlie Kelman’s shot proved to be the only goal of the contest as Orient claimed their first points of the season.
The defeat means Reading drop down to 12th in the table having been beaten at home for the first time since March.
With a big call to make in goal after Joel Pereira’s injury, Ruben Selles opted to start 21-year-old Coniah Boyce-Clarke ahead of the experienced David Button.
Wolves loanee Chem Campbell was handed his Reading debut, while Harvey Knibbs returned to the bench having missed several weeks with injury.
Reading started slowly which would set the tone for their performance in the opening 45 minutes.
The Royals only managed two shots on goal, the first of which was a tame header at the back post from Kelvin Ehibhatiomhan.
The second of which was a much more testing effort as Lewis Wing came close to scoring a trademark long ranger but saw his free-kick tipped behind for a corner.
Orient started to take more control in the contest and Dan Happe flashed a half volley a few inches off the target to give Reading a scare.
Boyce-Clarke made a strong reaction save from Charlie Kelman to palm his powerful strike over the top.
But just moments after that stop, Boyce-Clarke had a moment to forget as Kelman’s drilled effort, which was placed straight at the keeper, found the net after he let the ball squirm under his body.
Things could have got worse for Reading when a Tyler Bindon headed clearance looked to have struck the arm of Lewis Wing in the box, but the referee waved away any appeals for a penalty as the hosts went into the break trailing by a single goal.
Debutant Campbell nearly marked the occasion with a goal when he feigned to shoot to sit a defender down in the box, but then had his effort stopped by goalkeeper Zach Hemming with subsequent rebounds then blocked by a wall of Orient bodies.
Reading were beginning to knock on the door and a speculative strike from Michael Craig smacked the outside of the post, nearly catching the keeper out.
Selles made a double switch with 30 minutes to play as Harvey Knibbs and Adrian Akande replaced Savage and Campbell.
Another roll of the dice from Selles with less than 10 minutes to go saw Jayden Wareham and Kelvin Abrefa come on for Ehibhaitomhan and Craig.
However, Reading were unable to cause their visitors much trouble in search of an equaliser.
Up next for Reading is an away trip to Bolton Wanderers next Saturday.
Reading: Boyce-Clarke, Craig, Mbengue, Bindon, Dorsett, Savage, Wing, Elliott, Ehibhatiomhan, Campbell, Smith
Subs: Button, Abrefa, Dean, Knibbs, Wareham, Garcia, Akande
Leyton Orient: Hemming, James, Happe, Agyei, Brown, Currie, Beckles, O’Neill, Galbraith, Kelman, Clare
Subs: Howes, Simpson, Graham, Ball, Donley, Pratley, Perkins
Goals: Keman 27’
Attendance: 12,952,
Away: 941
