Paul Benson struck 11 minutes from time to earn Dagenham maximum points in a mid-table battle at Cambridge.
Three second-half goals livened up an otherwise dour clash with first Michael Morrison fouling Benson in the area and Chris Moore netting the penalty (55).
Mark Peters then got his head to Jon Brady's corner to equalise for Cambridge four minutes later.
The game looked to be heading for a draw until Benson rose to meet Danny Foster's cross and head in the winner.
Cambridge Utd: Howie, Gleeson, Morrison, Peters, Jaszczun, Brady, Hanlon (Smith 87), Quinton (Onibuje 45), Wolleaston, Pitt, Guy.
Subs Not Used: Heeroo, Davies, Waite.
Goals: Peters 59.
Dag & Red: Roberts, Foster , Vickers, Blackett, Griffiths, Saunders, Bruce, Southam, Mackail-Smith, Moore, Benson (Akurang 88).
Subs Not Used: Batt, Lettejallon, Kenny Clark, Hogan.
Booked: Benson, Foster .
Goals: Moore 55 pen, Benson 79.
Ref: C Evans (Lincoln).