Not since 1973 have the Royals been so tough to beat, although on this occasion the Yorkshire side made their task easier by fielding a virtual reserve side.
Kitson struck twice after the break to send Neil Warnock's side back to Yorkshire to concentrate on a push for the Barclays Premiership that sees them lead the Championship table with Reading on their coat-tails.
The first half left little to be remembered by although United seemed fortunate to survive a penalty appeal in the 13th minute when Steve Sidwell went down under Simon Francis' challenge.
The majority of the few chances that were created fell to the home side, with John Oster firing an early free-kick over and Sekou Baradji scuffing wide from a half-cleared corner soon after.
Nigerian forward Eric Obinna was desperate to impress Royals boss Steve Coppell and showed fine control to get the better of Francis in the box but could not beat goalkeeper Phil Barnes at his near post with a fierce drive.
The penalty appeal arrived seconds later but United's unfamiliar arrangement settled quickly after that and began to apply a little pressure at the other end.
Jonathan Forte was close with a drive but Colin Marrison sent an effort so off target it went for a throw-in.
Ian Ross was much closer with a long-range shot and it was not until the 45th minute that the Royals roused themselves to reply with first Sidwell and then Kitson heading over.
Forte almost broke the deadlock five minutes into the second half with a fine solo run that saw him motor past Ibrahima Sonko in the box and fire just over.
Obinna's response was a header that Barnes was able to hold before Kitson opened the scoring in the 53rd minute with a smart first-time finish from a free-kick move.
Stephen Hunt whipped the ball in from the left, Ivar Ingimarsson headed into the on-rushing striker's path and he buried it past the helpless Barnes.
Ross wasted a good equalising chance by failing to hit the target after Baradji had carelessly surrendered possession but there was a let-off for United when an unmarked Kitson stabbed wide at full stretch at the near post after Michael Tonge had surrendered possession.
Kitson picked up a 67th-minute booking for clattering Ross but after Obinna and his strike partner had come close with headers Blades substitute Nicky Law fired a good chance wide at the other end.
Kitson made the youngster pay straight away with the clincher in the 76th minute, extending a leg to poke home a ball across the box from Obinna after the United back line had struggled to cope with another Hunt delivery.