Jay Simpson gave the O's an early lead, and sent the hosts two goals ahead going into the break with a second strike in first half stoppage time.
Two goals with in the space of a minute however saw Dagenham level the tie through first Jamie Cureton and then Clevid Dikamona on the hour, before Armand Gnanduillet won it for the O's on the 65th minute with a powerful finish from Blair Turgott's cross.
Looking to end a run of four matches without a win, Leyton Orient made four changes to the side that lost at Barnet the previous weekend.
Captain Mathieu Baudry returned to the starting XI, along with Sean Clohessy, Blair Turgott and Armand Gnanduillet.
Kevin Nolan had been ruled out with an ankle injury earlier on in the day, while Peter Ramage, Calaum Jahraldo-Martin and Ollie Palmer all dropped to the bench.
Keen to get off to a positive start, Orient achieved just that and grabbed a third minute lead when a quick throw was flicked on by Armand Gnanduillet for Sean Clohessy who then fizzed a low ball across the six yard box for Jay Simpson to sweep home his 24th goal of the season.
Simpson could then have claimed his second of the afternoon soon after when a good move ended with Blair Turgott playing in into the forward on the edge of the area, but his shot was easily held by Mark Cousins.
The O’s had dominated the opening stages and Gnanduillet then spurned a wonderful opportunity as he ignored options in the form of Turgott and Simpson to both his left and right and dragged a shot wide of the mark from 25 yards.
Alex Cisak had yet to be troubled in the O’s goal throughout the opening 20 minutes, but was soon called into action as he parried Justin Hoyte’s shot from the edge of the area before smothering the ball at the second attempt.
There was a brief moment of panic for the hosts when Nicky Hunt sliced a clearance inside the O’s penalty area towards Daggers striker Christian Doidge, but Cisak reacted well to keep out the strike with his feet.
One minute stoppage time was indicated by the fourth official, and the O’s half time team talk was made a lot easier as Simpson registered his 25th goal of the season with a close range finish to convert Turgott’s cross.
Following the break both sides returned for the second half unchanged, and Simpson was denied the matchball on the 52nd minute when he curled a shot beyond the dive of Cousins before seeing his attempt crash back off the post.
As the hour mark approached Dagenham capitalised on a defensive error to pull a goal back as Mathieu Baudry’s weak header back to Cisak was pounced on by Jamie Cureton who then rounded the goalkeeper to slide the ball into an empty net.
A minute later the visitors were then level as defender Clevid Dikamona crashed home a volley from outside the box, much to the shock of the home fans.
Having seen their two-goal lead disappear in such swift fashion, Orient did not have to wait long to restore the lead as another Turgott cross was powerfully swept home by Gnanduillet with 25 minutes left to play.
That was to be the striker’s final piece of action for the O’s as he made way for Palmer, and the substitute almost added his name to the scoresheet straight away with a powerful header which was brilliantly parried away by Cousins.
Palmer was then denied once again 13 minutes from time when, despite managing to lift a shot over Cousins, Joe Widdowson was able to get back in time and head the ball off the line for a corner.
With eight minutes remaining Jack Payne was brought on in place of Nigel Atangana, and his midfield partner Lloyd James saw his effort deflected behind for a corner late on as he looked to seal the victory.
Dagenham were refusing to give up, and with two of the five minutes stoppage time played Cisak had to be at full stretch to claw away Matt Richards free-kick.
Cisak was to be called into action with only seconds left of the allotted time, wonderfully denying Joss Labadie from point blank range and preserve the O's lead.
There was still time for Simpson to try and claim his hat-trick however, as Palmer led a counter-attack and Orient's top scorer saw his shot parried by Cousins before Turgott's follow up was deflected wide in what was to be the final piece of action.
The result keeps Orient in the Play-Off race but still two points off, and unfortunately confirms Dagenham's relegation from League Two.
ORIENT: Cisak, Hunt, Baudry (C), Brisley, Binnom-Williams, Clohessy, James, Atangana (Payne 82), Turgott, Gnanduillet (Palmer 66), Simpson
SUBS: Sargeant, Ramage, Jahraldo-Martin, Koroma, Kashket
GOALS: Simpson (3 & 45+1), Gnanduillet (65)
DAGENHAM: Cousins, Hoyte (Pennell 66), Hyam (Taylor 47), Dikamona, Widdowson, Cash (McClure 74), Labadie (C), Richards, Hemmings, Doidge, Cureton
SUBS: Moore, Boucaud, Chambers, Hawkins
GOALS: Cureton (59), Dikamona (60)
BOOKED: Labadie (70)
REFEREE: Dean Whitestone
ATTENDANCE: 5,696 (444)