A brace from Charles Clayden and an Eric Lopes goal ensured the O’s completed the double over The Posh.
The reverse fixture ended also ended 3-1 to Orient when Ruel Sotiriou bagged a brace before Teddy Perkins sealed victory in Peterborough.
The O’s got the game underway and came close when Eric Lopes’ deflected shot looped just over the crossbar inside the first three minutes of play.
Lopes then linked up well with Charles Clayden who gave the O’s the lead on six minutes when his left footed strike from outside the box flew in to the top corner.
Despite the hosts enjoying the majority of possession; a long ball over the top caught the Orient defence out as the Peterborough striker raced through on goal, but for Sam Amedu who rushed out and beat the forward to the ball, clearing the danger in the process.
Midway through the first half Amin Benyoucef battled well to win possession back in the opposition half and the midfielder then beat two players but saw his shot bounce just wide of the post.
10 minutes of the first half remained when Peterborough equalised from the spot, Amedu guessed the opposite way and the O’s needed to respond quickly to restore their lead. It almost came through Andrew Camilo-Tayaca who saw an effort fly wide of the post after he raced down the wing and in to the box.
Mason Hall had a header at the far post chalked off for offside after Clayden’s whipped free-kick found he central defender in the box.
The ball was in the back of the net minutes later, this time through Lopes who collected the ball and darted in to the box before his dinked effort flew out of the ‘keepers reach and in to the goal.
Orient picked up where they left off in the first half when Clayden watched his effort whistle passed the target after some great work down the left wing.
A rare Peterborough attack saw Amedu spill the initial shot which gave the striker a second attempt on goal, which Camilo-Tayaca raced back to smartly clear over the crossbar for a corner.
Clayden collected Hector Kyprianou’s flick on, the winger then carried the ball before he chipped the Posh ‘keeper from 18-yards out to stretch the lead to 3-1, sealed the victory and secured the three points for the O’s.
ORIENT: Sam Amedu, Andrew Camilo-Tayaca, Shadrach Ogie, Mason Hall, Alfie Fleming, Hector Kyprianou, Ernold Haxhiu, Amin Benyoucef, Charles Clayden, Luca Carter-Henry, Eric Lopes
SUBS: Brendon Shabani, Jaedon Phillips, Will Sanders
GOALS: Clayden (2), Lopes