Halford's winner was his eighth goal of the season
Sheffield United overcame Preston to book their place in the Championship play-off final courtesy of Greg Halford's second-half header.
An edgy game saw chances at a premium before Halford rose above Youl Mawene to power home Kyle Walker's deep cross.
Preston threw men forward and Jon Parkin tested Paddy Kenny before Brian Howard cleared off the line from Neil Mellor's six-yard drive.
But United held firm with some stout late defending to progress to Wembley.
Kevin Blackwell's side were rewarded for their attacking intent and now find themselves just one game away from a return to the Premier League, two years after they were controversially relegated.
A rousing chorus at Bramall Lane raised the pre-match temperature to boiling point but despite the home side's superior possession early on there were few clear cut chances in a forgettable first half.
David Cotterill and Kyle Naughton peppered the Preston penalty area with crosses but centre halves Sean St Ledger and Mawene proved more than capable of mopping up anything that United threw at them as the visitors looked to soak up pressure and strike on the break.
The best chance of an edgy first-half fell to Howard, who found space 20 yards from goal only to drag his shot wide of the post
The second half started with a higher tempo from both sides and United striker Craig Beattie had an early chance as the Preston defence parted for him but he scuffed his shot wide from the edge of the box.
United, the only side showing any real attacking intent, began to be rewarded for their pressure with more chances as Beattie forced the first meaningful save of the game when his downward header was well saved by Lonergan.
Finally the home side made the breakthrough as Walker's inch-perfect cross found Halford and the tall midfielder, on a season-long loan from Sunderland, out-jumped Mawene and powered a header past Lonergan.
The goal woke Preston from their defensive slumber, with Parkin's snap-shot testing Kenny for the first time in the game before Howard cleared off the line from substitute Mellor's low shot.
United also had an effort cleared off the line when Beattie burst through, St Ledger did well to stop the ball going into the net.
With the minutes ticking away Preston threw caution to the wind and committed men forward but last-ditch defending from the home side reduced North End to half chances and sent Kevin Blackwell's men to Wembley for their fourth play-off final in 12 years.
Sheffield United manager Kevin Blackwell: "A lot of people have contacted the club in the last few days and there have been a lot of emails, because they feel it would right a wrong.
"It's been sorted out, but it's still festering among football people who feel things weren't right.
"I don't think that sits well with people in English football and most of the fair-minded supporters, so if we can get that right it would go a long way tolancing the boil totally."
Preston manager Alan Irvine: "We wanted to go the next step and then the one after that, so we're all clearly very disappointed.
"I can't speak for previous play-offs and it wasn't down to luck this time in any case.
"Sheffield United were better than us in both games and deserved to go through overall."
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