Spartans went ahead on eight minutes as JJ O’Donnell flicked a Nicky Deverdics free-kick into the bottom corner, before McNall headed home his first competitive club goal ten minutes later to double their lead.
Luke Charman pulled one back for Darlington two minutes before half-time. Substitute Andrew Nelson completed the comeback from close range just after the hour mark.
Nelson made three changes to the side that drew with Brackley, with Alex Mitchell returning in goal, and Jordan Hickey and McNall replacing the suspended Cameron Painter and injured Dan Maguire.
The 1,530 fans packed into Croft Park were treated to a lively start, as McNall put the Darlington defence under pressure with a dangerous run within the first few seconds. Then Will Hatfield threatened for the visitors as he saw an effort well blocked by Jordan Hickey before forcing Mitchell into a save with a low drive.
While Blyth have struggled to make the most of their dominance in recent matches, this time they took the lead with their first effort of the game. Deverdics whipped in a trademark free kick from the left which was met by the head of O’Donnell, whose header nestled into the corner.
Despite the setback, the Quakers began to look dangerous as they began to dominate possession, forcing Toby Lees into a great block to deny Josef Wheatley, before Lees and Sean Reid were on hand with brilliant defensive headers.
However, as good as they were going forward, Darlington were lacking defensively and Blyth made the most. Karl Byrne found space on the right wing and picked out McNall, who made no mistake and directed his free header into the bottom corner to double Spartans’ lead.
Charman thought he’d pulled one back on 25 minutes, only to be denied by the linesman’s flag.
That looked to be the closest the visitors would get as Blyth kept them at bay, only for Charman to score a fine goal out of almost nothing.
The former Newcastle striker picked the ball up on the edge of the box, weaved his way past a couple of Spartans defenders before firing low past Mitchell to give the visitor’s hope going into the break.
It was a quieter opening to the second half, but Mitchell had to be alert as he denied Charman with a brilliant point blank save after the ball broke to the striker in the box.
That seemed to spark the game back into life, as Spartans thought they had increased their lead as Reid fired home, only for the goal to be chalked off, again for offside.
Just a few minutes later Blyth’s misery was compounded as Darlington found themselves level. Within two minutes of coming on Nelson fired home following a goalmouth scramble, after the visitor’s clattered a header off the crossbar.
Spartans were straight up the other end, but Deverdics could only fire his effort high and wide after finding space on the edge of the box.
From then on opportunities were at a premium for both sides as the game turned into a scrappy affair in the closing stages.