Skipper Mark Arber put the home side ahead in the eighth minute when he lost his marker in the Rochdale box to nod past a statuesque Frank Fielding.
Daggers striker Paul Benson thought he had doubled the lead two minutes later when he headed into the net, only to see the goal ruled out after he was judged to have fouled defender Nathan Stanton.
Dale pressed for an equaliser, and their efforts finally paid off in the 16th minute when Tom Kennedy slotted a curling free-kick low past Daggers goalkeeper Tony Roberts from the edge of the box.
The visitors were buzzing and took the lead in the 21st minute when Adam Le Fondre clipped a clever back-heel across the face of goal for Nicky Adams to prod the ball past Roberts from point-blank range to score on his debut.
Talented Dale striker Will Buckley nearly capped a sparkling first-half display when he swerved past Arber into the Daggers area, only to fire a weak shot straight at Roberts from ten yards.
Rochdale caught Daggers napping in the 57th minute, with skipper Gary Jones firing against the post after losing his marker on the edge of the box.
Daggers threw men forward in search on an equaliser and finally found one in the 74th minute when Ritchie raced on to a misplaced header on the corner of the Dale area before lashing an unstoppable strike across Fielding and into the net.
Dale were rocking - and the home side capitalised on yet more shaky defending in the 79th minute when midfielder, Glen Southam, showed superb technique to volley past Fielding from close range to give his side the lead.
Saunders blotted his copybook when he was sent off for kicking out at Buckley right in front of the referee in the 87th minute.
Rochdale tried to mount a comeback but had nothing left in the tank, with Daggers holding on for a deserved win.