A first-half goal from Bury striker David Amoo heaped the pressure on Preston manager Phil Brown.
The visitors have now lost their last four matches and their winless run has been stretched to 13 games.
Amoo scored 15 minutes into the game on the counter-attack, as he outpaced the defence to latch onto a perfectly-judged ball from Peter Sweeney.
Preston, who are now without a goal in four matches, went close in the second half through Neil Mellor.
Amoo had chances to extend Bury's lead but had a header cleared off the line and two further shots saved by goalkeeper Thorsten Stuckmann.
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Bury manager Richie Barker told BBC Radio Manchester:
"We were asking for back-to-back wins and we've gone one further. If I'm honest, beyond the three points I thought we were excellent.
"I thought we could have won it more comfortable than it was, as whenever it's 1-0 you're always susceptible to breakaway goal or a corner.
"I thought he [David Amoo] was excellent. He carried the ball, got us higher up the pitch and he's weighed in with a goal."