Keith Treacy's spectacular second-half double boosted Preston's survival bid.
But a 3-1 defeat dealt a huge blow to Sheffield United's hopes of avoiding relegation from the npower Championship.
The Republic of Ireland winger, who had a spell on loan at Bramall Lane last season, opened the scoring in the 55th minute with a speculative long-range shot and then added a second from distance 13 minutes later.
United hit back through Jordan Slew with 18 minutes remaining but North End substitute Nathan Ellington added a late third as Phil Brown's side moved four points ahead of the Blades.
The result condemned Micky Adams' side to a fourth straight defeat but was a massive boost to Preston as they recorded their third successive home victory.