Preston captain Kevin Nicholls was put clean through in the fourth minute but his close-range shot was parried by Owls keeper Lee Grant and the danger was cleared.
Andy Carroll, on loan from Newcastle, had an eight-yard header saved from Callum Davidson left-wing cross.
Wednesday captain Steve Watson was booked for tripping Carroll 40 yards from goal after 12 minutes.
The Preston goal came after 28 minutes when Carroll had a 12-yard shot from the right, which Grant could only parry and Paul Gallagher, on loan from Blackburn Rovers, ran in from the left to knock in the rebound left-footed from close-range into the bottom right-hand corner of the net.
Carroll had another shot saved and Darren Carter had a 25-yard effort pushed around the post for a right-wing corner.
Etienne Esajas had an 18-yard left-foot shot from which hit the left-hand post after 48 minutes and the ball bounced out into open play and was cleared.
Watson had a 12-yard left-footed shot saved by Preston keeper Andy Lonergan and Carroll had another header saved by Grant, who pushed the ball around the post for a right-wing corner.
Gallagher was booked for a foul on Wade Small but stayed down injured and had to be substituted by Simon Whaley.
Glenn Whelan had a shot cleared by Youl Mawene for a right-wing corner and Francis Jeffers saw his effort saved as was Esajas' follow-up shot.
Youl Mawene was booked for a foul on Wednesday player Akpo Sodje after 67 minutes.
Owls player Jermaine Johnson was booked for a foul on Preston's Chris Sedgwick towards the end but Preston hung on for an important three points.