A brace by Romain Vincelot sunk Orient and secured Daggers a maiden win of the season in this first-ever League One derby between the east London sides.
Vincelot struck early in each half at Victoria Road as Orient looked in vain for a cutting edge and were punished for starting slowly.
The Daggers were worthy winners of this contest, the result of which has the teams level in the table, on four points each.
Orient had a wealth of corners and plenty of possession, but Daggers shut up shop as the game wore on for the three points.
Daggers came out the traps fast and made sure danger-man Danny Gr een had enough of the ball to do damage. Orient were put on the back foot and struggled in midfield to make an impression.
Daggers soon made home advantage count. Green's sweeping cross from wide right was not dealt with and Romain Vincelot stole in between Orient shirts and netted from close -range.
Dean Cox posed most threat for Orient as the visitors began to get a grip on the game, but little went right for the O's during a frustrating first half. In contrast, Daggers' passing was crisper and more incisive, with Gavin Tomlin and Josh Scott posing a threat playing off the shoulder of the O's defence.
They caused problems throughout amid some uncertain defending by Orient inside their area.
But it was not one-way-traffic. The O's had a string of corners without making one count. Tony Roberts in goal save superbly Alex Revell's header on 42 minutes from Spring's corner.
Vincelot, presaging what would soon follow, fired just over for the Daggers from long-range as half-time loomed.
Then he was on target again five minutes after the restart. His header doubled the advantage at close-range from Mark Arber's headed lay-off across the goal-mouth.
Revell went close with a header of his own soon afterwards from Cox's cross. Orient then had cries for a penalty waved away after Vincelot's arm was struck by Chambers' shot during a spell of pressure by Orient.
Orient were vulnerable under pressure and Josh Scott's shot rattled nerves and the crossbar, on 71 minutes. Alex Revell drew a fine diving save from Roberts minutes later with a curler, as the game slipped away from Orient.
A good day to be a Daggers fan, and they made sure Orient's followers knew it, too.
Leyton Orient: Jones (gk), Omozusi, Chorley, Forbes, Cox, Dawson (capt), McGleish, Chambers (Jarvis 71), Revell, Spring (Patulea 89), Smith.
Unused subs: Butcher (gk), Brown, Porter, Cestor, Beautyman.
Daggers: Roberts, McCrory, Doe, Arber (capt), Green, Scott, Tomlin (Nurse 81), Currie (Lewis 78), Ogogo (Antwi 45), Vincelot, Gain.
Unused subs: Lewington (gk), Mongomery, Bingham, Gwillin.
Attendance: 4,195 including 1,199 Orient fans.
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