Alan Thompson was in charge, and United scored after three minutes through Wesley Ngo Baheng.
The Northern League side drew level on the half-hour mark, Forster losing his hold when coming to claim a right-wing corner allowing Douglas to arrow home through bodies from 10 yards.
Toon Reserves Win At Ashington!
Zamblera made it 2-1 to the the Toon just before half-time from point-blank range.
Ashington scored 10 minutes after the break when former Magpie youngster Liam Atkin guided a low 12-yard shot past Ole Soderberg.
Substitute Ameobi shot left-footed into the bottom corner after good work from Swedish wideman Samuel Adjei to win the game.
NEWCASTLE UTD RESERVES: Fraser Forster (Ole Soderberg, 46m), James Taylor (James Tavernier, 62m) Callum Morris, Ben Tozer, Darren Lough, Jonny Godsmark (Phil Airey, 46m) (Samuel Adjei, 53m), Frank Danquah, Patrick McLaughlin (Brad Inman, 62m), Ryan Donaldson, Wesley Ngo Baheng, Fabio Zamblera (Sammy Ameobi, 46m)