Brian Howard's goal sent Sheffield United into second place and dented Reading's automatic promotion hopes.
Howard converted from close range after Matthew Kilgallon's header had come off the crossbar and fallen into his path.
Seconds earlier Reading's Dave Kitson headed Jimmy Kebe's cross against the bar while the striker also forced a fine save off Paddy Kenny soon after.
Reading's Kalifa Cisse and Sheffield United's Jamie Ward were stretchered off after separate incidents.
The Blades climb into second on goal difference above Birmingham, who have a game in hand against rock bottom Charlton on Saturday.
Reading manager Steve Coppell: "Our home form is a massive worry. It is giving me sleepless nights and I have got to get home for another one of those now.
"It's something which is bemusing. To be so strong for so long and now we have lost four and drawn two of the last six here baffles me.
"I don't know what's going on or else I would have changed it."
Sheff Utd Kevin Blackwell:
"It's another win on the long road to the Premier League but that's all it is.
"We knew it would be tough here against an excellent Reading side and that proved to be the case.
"If my players were not such strong characters then they would not have won that game but they have been phenomenal for me all season.
"Of course psychologically it is a boost for us all to be in the top two but we have four games left.
"I would like to go second on the last day of the season if it was down to me but it's not down to me."
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