United opted against playing out-of-favour first-team star Hatem Ben Arfa at Croft Park, but Olivier Kemen, Gael Bigirimana and Northern Ireland international Shane Ferguson all featured.
Gael Bigirimana
A goalless first half had seen Blyth dominate as they hit the woodwork twice, but United were much better at the start of the second period.
Newcastle grabbed the lead mid-way through when Ferguson crossed from the left and striker Tom Heardman converted from close range to break the deadlock on 63 minutes.
But Blyth levelled things up with 15 minutes to go when a right-wing cross was met by Robbie Dale who sent a towering header past Woodman.
Full-back Greg Olley thought he was the hero when he headed home after a left-wing cross with 10 minutes left before the late goal rush of an entertaining game.
Jarrett Rivers scored a screamer to level the game at 2-2 with just four minutes left.
But the Magpies won it in the dying stages when Liam Smith smashed home to deny Blyth a draw.
BLYTH: Jeffries, Nicholson, Watson, Parker, Buddle, Sayer, Wearmouth, Hooks, Maguire, Robinson, Dale.
UNITED: Woodman, Olley, Ferguson, Kemen, Williams, Gillhespy, Roberts, Bigirimana, Heardman, Quinn, Smith.