But basement boys Mansfield town put up a battling performance and Giles Coke's goal midway through the second half almost threw them a lifeline.
Orient, looking to record there third straight victory, started well and skipper Gary Alexander missed a golden chance after just 8 minutes.
Mansfield, despite there lowly position, always looked dangerous on the break and home goalkeeper Glyn Garner had to parry a snap shot from the lively Simon Brown.
But it came to no surprise when Orient took the lead on 16 minutes. Gary Alexander sent Shane Tudor scurrying down the right and his pin-point cross was smashed home from close range by Joe Keith at the far post.
Gareth Jelleyman almost levelled three minutes later when he raced clear of the home defence but he rolled his shot agonisingly wide.
As the game swung from end to end a Keith cross cannoned off the woodwork as Orient almost stretched their advantage, while the hugely impressive Coke shot inches wide after a stunning solo run.
After the break Mansfield threw substitute Adam Rundle into the fray and he should have fired a leveller when he found himself in the clear but sent his shot narrowly wide.
It was a costly miss as, shortly afterwards, Matthew Lockwood's free-kick bounced off the chest of Mansfield's veteran goalkeeper Kevin Pressman and the ball rebounded into the net off defender Alex Baptiste - despite Orient's top scorer Alexander claming the last touch.
The visitors threw themselves a lifeline midway through the half when Brown's shot took a deflection and smacked against the Orient bar with Coke following up to gleefully head home the rebound.
Baptiste went close to a leveller before Orient sub Echanomi wrapped things up within 60 seconds of replacing Jabo Ibehre.
He latched on to Tudor's pass, outpaced the Mansfield's defence and fired past Pressman to lift Orient to second place in the table.