The former Stevenage wide man, signed for £260,000 last month, sent a 74th minute half volley screaming past Boston 'keeper Andy Marriott from fully 35 yards after Boston had grabbed the lead on 61 minutes through Nathan Joynes and looked to be heading for an unlikely win.
Boston, so short of players they could only muster four substitutes, suffered a further blow before the half-hour when their injury jinx struck again with skipper Paul Ellender having to be replaced by Stewart Talbot after coming off worst in a clash of heads with Posh defender Sean Blackett.
With few clear cut openings before the break, the most worrying feature for a local derby tussle was a total lack of atmosphere. But in all honesty there was precious little for a crowd of just under 5,000 to cheer.
Pilgrims striker Drewe Broughton turned defender to head away a Jamie Day free kick after Stephen Vaughan fouled Josh Low. Ex-Posh man Broughton also forced Craig Morgan and Blackett into mistakes at the other end, although the nearest Boston came was a Jamie Stevens effort that drifted wide of Mark Tyler's goal.
Tyler was alert enough to advance and snatch the ball away from Joynes but as Posh improved Craig Mackail-Smith, making his first start after a move from Dagenham and Redbridge, headed over after doing well to reach a cross that came at the end of a penetrating run from Adam Newton.
Joynes, on loan from Barnsley, broke the deadlock just after the hour, jinking through to leave Tyler and defender Mark Arber on the deck before poking in Boston's first goal in over 400 minutes of football.
Crucial substitutions to introduce Boyd and Peter Gain helped Posh to turn the game with Boyd's strike setting up a grandstand finish that saw Danny Crow, Josh Low and Boyd himself all go close before Morgan rattled the Boston bar from 20 yards in added time.