The Lilywhites had lost their first three league games of the campaign heading into the weekend, but a battling performance from Frankie McAvoy's side secured all three points in Lancashire.
Preston created a string of chances to kill off the game after the break, but Patrick Bauer's early goal proved enough to condemn Darren Ferguson's side to a first defeat since the opening weekend of the season.
Neither side were able to create much in attack amid rainy conditions in the early stages before Bauer's firm header edged the hosts in front after 14 minutes.
Ryan Ledson's whipped free-kick from the left exposed some poor Peterborough set-piece marking around the penalty spot and Bauer got up above his man to power a finish past Christy Pym.
That key breakthrough handed the home side the initiative and a vital confidence boost as they pushed hard for a second goal before the break.
Daniel Johnson's curled effort from 25 yards drifted just wide before the Jamaican international's dipping cross was flicked on to the top of the crossbar by a stretching Ben Whiteman after 34 minutes.
Despite struggling to threaten in the opening 45 minutes, Peterborough almost produced an instant equaliser immediately after the restart.
Siriki Dembele's mis-hit shot caused chaos inside the Preston box, with Sepp Van Den Berg making a key block on the six-yard line before Andrew Hughes eventually hacked away the loose ball.
That frantic start to the second period set the tone for the closing stages as both sides pushed forward.
Scott Sinclair's driving run took him clear of two Peterborough challenges on the edge of the area, but Pym's sharp reactions kept out the former Celtic star, with Whiteman hammering narrowly wide from the rebound after 57 minutes.
Peterborough responded as Jonson Clarke-Harris' snapshot was beaten away by Daniel Iversen as the Preston defence was caught out.
Despite Peterborough's occasional threat on the break in the final half-hour, it was McAvoy's under-pressure side that looked more likely to find the next goal.
Pym was again called into vital action to tip over Hughes' towering header after Bauer's knockdown at a corner before the overworked keeper produced a diving save to deny Danish winger Emil Riis Jakobsen.
But one goal proved enough for Preston to pick up their first home win since May 1.