Jon Ashton's 54th-minute header proved decisive as Grays held on to seal victory over Altrincham.
The defender met Charley Hearn's left-wing cross to nod home and seal victory for the visitors.
Grays could have made it a much more comfortable win but striker Danny Kedwell saw his feeble penalty easily saved by keeper Richard Acton.
However, Altrincham's dismal afternoon was sealed when striker Colin Little was dismissed for violent conduct.
Altrincham: Acton, Lane, Scott (Aspinall 49), Tinson, Munroe, Lawton, Owen, Whalley (Potts 75), Peyton, Little, O'Neill (Thornley 77).
Subs Not Used: Rose, Senior.
Sent Off: Little (86).
Booked: O'Neill, Lane.
Grays Athletic: Flitney, Sambrook, Cooksey, Stuart, Ashton, Lawson (Gross 90), Hearn, Barnard, Oli, Watson (O'Connor 60), Kedwell (McAllister 87).
Subs Not Used: Knowles, Day.
Goals: Ashton 54.
Att: 807.
Ref: R Merchant (Staffordshire).
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