The on-loan Peterborough striker completed an unlikely triumph by grabbing the winner just two minutes after Jonson Clarke-Harris had equalised.
Bury's relegation had been confirmed by defeat to Oldham three days previous but they recovered sufficiently to leave Scunthorpe perilously close to the same fate.
The visitors had actually started much stronger, Matt Godden springing the offside trap only to shank a tame effort wide.
Cameron Belford made an acrobatic save from Karl Hawley's deflected effort but could do nothing about the Iron striker's header on the stroke of half-time.
Hawley glanced an expert finish into the corner of the net from Mark Duffy's arrowed cross.
Duffy spurned a good chance to double the lead, allowing Clarke-Harris to level with a stunning left-footed free kick, which flashed past a stunned Eirik Johansen.
The Shakers completed their comeback when Ajose capitalised on a defensive mix-up to slot home, leaving Scunthorpe five points from safety.