Dagenham went six points clear at the top of the Conference but were made to work hard by struggling Grays.
Craig Mackail-Smith latched on to a long clearance by goalkeeper Tony Roberts on 11 minutes to score with a low 18-yard shot.
Grays, without a win since October, could have levelled before the break but for two great saves from Roberts.
He twice denied Lee Boylan and did so again near the end before Mackail-Smith spurned a chance score his second.
Grays Athletic: Bayes, Sambrook, Cowan, Stuart, El Kholti, Williamson, Poole, Harding, Bodkin (Martin 73), Boylan, O'Connor (Turner 67).
Subs Not Used: Knowles, Smith, Nicholls.
Dag & Red: Roberts, Griffiths, Uddin, Foster , Leberl, Rainford, Southam, Blackett, Benson (Akurang 60), Saunders (Sloma 87), Mackail-Smith (Strevens 81).
Subs Not Used: Hogan, Cole.
Booked: Roberts, Rainford.
Goals: Mackail-Smith 11.
Ref: G Scott (Devon).