The visitors struck with two stunning goals from Rickie Lambert and efforts from Grant Holt and Alan Goodall to recall their second successive away win.
The victory was no more then Dale deserved, they started positively and took the lead on 24 minutes when Holt, who gave the Orient defence a torrid time, swept past Gaby Zakauni and fired home from 10 yards.
It was the first time this season Orient had been behind and they almost levelled when Michael Simpson's 25-yard blast was parried by Rochdale keeper Matthew Gilks.
It would have been an undeserved leveller and the visitors responded by stretching their advantage on the half hour when Lambert curled a stunning free-kick from 25 yards around the Orient wall and into the top corner of Glyn Garner's net.
Tommy Jaszczun almost added a third just before the break but Garner saved well.
In the second half Orient tried hard to fight their way back into the contest but were denied by the rock solid Rochdale defence - and the visitors wrapped things up with a third with 22 minutes from time.
The ever dangerous Lambert broke clear and drilled an effort past Garner to give Dale a three goal cushion.
Orient's misery was completed six minutes later when a powerful Holt held the ball up in the penalty area and fed Alan Goodall who gleefully fired home from eight yards.
Orient grabbed a consolation effort 60 seconds later when substitute Justin Miller sent in a long throw from the right.
For the one and only time in the game the Rochdale defence hesitated and Orient's teenage substitute Efe Echanomi headed the ball home from close range - his second goal of the season.
But it was too little to late Orient's unbeaten record was in tatters.