Plymouth remain the only side to have beaten the Royals this season. That defeat came on the opening day with a last-gasp winner for the Devon side.
Neither Reading nor United were at full strength but Reading always had the upper hand with United getting just one shot on target all night. That came two minutes from the end.
Reading striker Dave Kitson scored twice in the second half to take his season's tally to seven. The first came when he lashed home Stephen Hunt's left-wing cross and the second from close range when he turned in Eric Obinna's cross from the right.
Reading also had a penalty appeal turned down when Steve Sidwell and Simon Francis clashed, but Hampshire referee, Rob Styles, waved play on as Sidwell sat on the ground with his arms raised in protest.
Reading made their intentions clear early on with John Oster firing a free-kick just over the bar, Stephen Hunt testing keeper Phil Barnes and Sekou Baradji shooting wide.
Blades manager Neil Warnock protested loudly when Oster was awarded a free-kick. Warnock felt he had dived and had to be quietened by the fourth official.
Moments later Obinna looked set to score Reading's opener but his fierce shot was well blocked by keeper Phil Barnes.
A lively start to the second half saw Jonathan Forte shoot just wide for United and at the other end Obinna had a header saved by Barnes.
A slip by Baradji let Forte in for another shot that sailed just wide of Graham Stack's right-hand post.
With the last attack of the first half Kitson headed over from Obinna's right-wing cross. It was a warning for United of the dangers that lay ahead of them in the second half.