Neil Warnock's side are yet to taste defeat this summer, but were made to work hard for the win.
Whites defender Tom Lees gave them the lead just after the half-hour mark with an excellent volley inside the penalty area.
But the visitors were stunned after the break when John Mousinho was able to run unchallenged before firing home a neat finish.
Lees' defensive partner Sam Byram restored the visitors' lead 10 minutes later when he converted Paul Green's cross.
And midfielder Aidy White sealed matters in the 80th minute with an excellent strike to leave Preston goalkeeper Thorsten Stuckmann with no chance.