The Blades carved out the chances but failed to put them away in a frustrating afternoon at Bramall Lane, before Ward struck his fifth goal of the season.
United, whose seven-match unbeaten run ended at Leicester on Boxing Day, started in emphatic manner, Ward's fierce strike blocked by Neil Collins before Henri Camara fired over the top from just inside the box.
The ex-Wigan striker has a better opportunity on 21 minutes, Richard Cresswell doing the hard work as Camara lashed in a low strike, the ball curling the wrong side of the far post.
Preston, with just one win from nine games, survived again after United won a free-kick 20 yards out, full-back Jordan Stewart threading the ball towards Camara as Andy Lonergan charged off his line to scoop up the loose ball.
Ched Evans, desperate for a goal on his 21st birthday fired a volley straight at the Preston keeper as United, in total control failed to cash in on their chances.
The lively Camara should have broken the deadlock minutes before the break, the opportunity carved out by full back Derek Geary, playing his first senior game in 18 months after recovering from a career threatening knee injury.
The little full-back picked out the United striker who broke into the box, pursued by Sean St Ledger but as Lonergan raced off his line Camara panicked looping the ball over the target.
Ward had a low cross smothered on the line by Lonergan before Preston at last began to exert pressure on the United rearguard. Stephen Elliott had a deceptive cross scooped up by Mark Bunn, before former United midfielder Michael Tonge fired in a right-foot strike on the hour.
Preston could have snatched all three points 11 minutes from time as United failed to cut out skipper Callum Davidson's precise cross from the left, Elliott rose unmarked, but glanced his header inches wide of the far post with Bunn beaten.
Ward had the final word on 87 minutes his angled cross from the left deceiving Lonergan as the ball curled over his head from 22 yards.