Centre back Colin Hoyle headed home his second goal of the week to earn Lynn the points in a dour encounter.
Hoyle, who had scored only once in 59 appearances, has now found the net twice in as many games.
His match winning goal after 13 minutes again came from a corner. It was Steve Williams who got the touch to Matthews' flag kick and allowed Hoyle to head powerfully in off the post.
It was a repeat of a similar move three minutes earlier when McNamara flicked on Matthews' kick for Lee Hudson to convert but the offside flag brought celebrations to a premature end.
Matthew Wright was again influential on the right wing but when he lost his way after the first quarter, so the game died and only a late burst of activity brought any relief for the 585 strong crowd,
James Hollman was recalled to action and the former Ipswich keeper had a steady game with two outstanding saves.
Hudson was twice denied by keeper Stuart Ford and Williams wasted a golden chance when he allowed Dave Robinson to catch him on the edge of the area when a goal beckoned.
A cheeky back heel by Wright allowed Hudson acres of space but Robinson recovered well to head behind while Gresley's sporadic attacks were easily dealt with by a solid Lynn rearguard.
Lynn: Hollman, Matthews, Skelly, Hoyle, Wright , Spearing, Pascoe,
Williams, Roberts, McNamara, Hudson. Subs: (not used) Ellis, Cambridge, Delicata
Gresley: Ford, Guyett, Horseman, Denby, Fitzpatrick, Robinson, Wardle, Wilson, Grant (Alsop 68) Davies, Fowkes. Subs (not used) Carvell, Mead.