It was a belated birthday present for Ferguson, son of Sir Alex, who was 35 on Friday, and ended a dire run for Posh who had not tasted victory since early December.
Ferguson spent seven years at the Racecourse Ground before getting the Posh job early in January and insisted this game was the opportunity for Posh to re-launch their season.
Something certainly had to give in a meeting of League Two's least in form sides and Wrexham, without a win in eight outings, had the better of the early exchanges against a Posh side that had not won in its 10 previous matches.
Wrexham should have grabbed the advantage when Lee McEvilly went for goal despite having Neil Roberts in close support. McEvilly was forced wide by Craig Morgan and failed to get a shot on target.
The bustling striker did send one drive inches wide of Mark Tyler's left-hand post after a flick on by Steve Evans but, by then, Wrexham were trailing to Aaron McLean's 22nd goal of the season and his ninth since joining Posh from Gravesend before Christmas.
The ever alert McLean gave John Ruddy no chance with a fierce low right-footed drive after Adam Newton's pace on the right was too much for Wrexham defender Mike Williams and his centre dropped kindly for McLean after coming off the heel of Evans.
Posh began the second period with a sustained attacking burst and the second home goal on 53 minutes was the first in league soccer for exciting left-wing prospect George Boyd. A £260,000 capture from Stevenage Borough, he buried a 20-yard drive in the far bottom corner of the net from the tightest of angles.
Danny Williams wasted a rare chance for Wrexham, producing a tame shot that held no terrors for Tyler, and the home domination was confirmed with eight minutes left when Evans headed into his own net after another break and teasing centre from the unstoppable Newton.