Under-par Whitby lost out on their chance to go top as hosts Grantham won the Blues’ game in hand on leaders Buxton.
Manager Chris Hardy made one change from the side that defeated Sutton Coldfield 2-0 on Saturday with a recall for left-wing-back Danny McWilliams in favour of Curtis Round.
The Seasiders started sluggishly and conceded a penalty inside six minutes when Kieran Weledji dangled a right leg inside the left edge of the Blues box and Luke Shaw went over it at the end of a mazy run.
However, goalkeeper Shane Bland had no problem saving low to his left from Danny Meadows’ soft spot kick.
The Gingerbreads, who went into the game with a record of just two wins and four defeats at the home, continued to press and on 15 minutes it took a brave block from Weledji to keep out Ben Saunders’ snapshot.
Moments later, Filipe Barcelos chipped inches over the crossbar, from 20 yards.
At the other end, a rare Whitby breakaway saw Luther Wildin swing a right leg at thin air and Dale Hopson, lurking on the left edge of the six yard box, turn against the outside of the near post.
The Seasiders began brightly after the interval, but the hosts looked well drilled, continually halting attacks on the edge of their box.
The Lincolnshire side then hit a sucker punch, seven minutes into the second half.
A right-wing cross was headed down for Ben Saunders to turn home with a six yard overhead kick.
Hardy threw on striker Mikey Roberts for midfielder Dave McTiernan, midway through the second period and Roberts’ effort on the break was charged down before he brought a brave near post parry from Jake Turner, who had done well to parry Callum Martin’s awkward free-kick, from the left.
By now, Round had replaced McWilliams but Whitby were well shackled for much of this game and the home side sewed it up, two minutes from time after an error.
Weledji was charged down as the visitors tried to Shepherd the ball away and substitute Lee Shaw, only on the field for six minutes, showed good composure to slot across Bland and inside the bottom right corner, from a tight angle.
Bland, Martin, McWilliams (Round 80), Weledji, Bythway, May, Gell, McTiernan (Roberts 68), Hopson, Tymon, Snaith (c). Subs not used: Robinson, Park, Dawson (GK).