It worked ... and the Mags won the cup ... but they did it the hard way.
0-0 after 90 minutes, Blyth who took the lead four minutes into extra time with a goal from Andrew Leeson.
But Kazenga LuaLua scored from 25-yards within seconds of Spartans taking the lead.
The game went to penalties and Mark Doninger scored the vital winner.
NEWCASTLE UTD RESERVES: Fraser Forster, Callum Morris, Darren Lough (Matthew Grieve, 91m) Mark Doninger, Ben Tozer, Tamas Kadar, Jonny Godsmark, James Troisi (James Marwood, 62m), Ryan Donaldson, Wesley Ngo Baheng (Frank Wiafe Danquah, 57m), Kazenga LuaLua
Subs not used: Ole Soderberg, Shane Ferguson