SUPERSUB Billy Sharp spared the Blades’ blushes at the Madejski.
The striker, 34, climbed off the bench 11 minutes from the end of the 90 — yet could not stop the Royals taking the tie to extra-time after a controversial penalty from George Puscas.
But Sharp’s extra-time header bagged Sheffield United a spot in the hat for tonight’s quarter-final draw.
After their return to the top flight, United are up to eighth in the Prem and dreaming of glamour European ties in Madrid or Milan.
It all makes Tuesday night trips to the Royals a faint memory.
But they quickly showed they had not forgotten how to mix it in the Championship, scoring in 85 seconds.
It was too easy as Luke Freeman raced forward and picked out Ben Osborn on the left wing.
He had time to pick out David McGoldrick with his cross — and the striker had a free header past Rafael Cabral from eight yards.
It was simple as you like for the Ireland striker, who celebrated his first club goal since April 22.
Reading had a chance to level when Yakou Meite’s shot was palmed away by Dean Henderson.
At the other end, Freeman’s corner was met by John Egan — but the Blades captain looped his header on to the roof of the net.
But as Sheffield United were settling in for half-time, Reading were handed a lifeline with a soft penalty just before the break.
Ironically, given this match was being shown live on Facebook in an FA Cup first, there was a Friend request — that’s ref, Kevin Friend.
With no VAR to overturn the decision, Reading appealed when Andy Rinomhota threw himself on the ground with barely any pressure from George Baldock.
The ref accepted it and Puscas, who joined for £8million from Inter Milan to become Reading’s record signing, thumped the ball past Henderson two minutes from half-time.
It was tough on the Blades, who were the better side in the opening 45 minutes and felt rightly aggrieved by ref Friend’s decision.
After the restart, Reading’s Michael Olise shot wide as they grew in confidence.
Royals boss Mark Bowen had already labelled this match as their “biggest game of the season” after a poor run in the league.
Reading had been on an alarming slump with just two wins in 11 league games to sit seven points above the drop zone.
But as they forgot about their dreadful league form they started to edge this Cup tie, with on-loan Chelsea defender Matt Miazga looking solid at the back.
Reading tried their luck again with an ambitious penalty appeal when Puscas went to ground in the box under pressure — but this time it was turned down by Friend.
Blades boss Chris Wilder had seen enough from his toothless side and brought on striker Billy Sharp.
It was defender Chris Basham who had a chance to put the Premier League side back in front — but his header was easy for Cabral.
With the clock ticking down on the 90, Henderson was at full stretch to claw the ball away from Ovie Ejaria.
But just before half-time in extra time, Freeman’s superb cross set up Sharp for an easy back-post header to leave the Royals heartbroken.