Sheffield United struck three late goals to sink Leicester.
Andy Gray put the Blades ahead after 34 minutes from the spot after Leicester keeper Rab Douglas fouled Paul Ifill.
David Connolly levelled for Leicester from close range five minutes after the interval, but Steve Kabba's penalty put United back in front after 80 minutes.
Ifill headed the third from Keith Gillespie's cross three minutes later, before Leigh Bromby bundled home a fourth in the last minute.
Leicester manager Craig Levein:
"The players can't believe how we lost that match 4-1, but I think the referee decided the outcome.
"The ball spun up and hit Nils-Eric Johansson on the shoulder. It's such a critical decision because it looked like we were going to win.
"It's such a critical decision, at such a crucial stage of the match, and it's cost us today because it looked like we were going to win the game and that was the turning point."
Sheffield United boss Neil Warnock on new signing Paul Ifill:
"I thought £800,000 was cheap because if we had beaten Wolves and gone up I was willing to pay £1.5m for him.
"I just think he's a special player and I don't think he knows what he's going to do next.
"The defender doesn't know and he's so direct and positive. I think he'll prove an absolute bargain for us."
Sheff Utd: Kenny, Bromby, Morgan, Jagielka, Harley, Ifill, Montgomery, Nalis, Tonge (Shipperley 78), Gray (Kabba 77), Webber (Gillespie 77).
Subs Not Used: Alan Quinn, Kozluk.
Goals: Gray 34 pen, Kabba 81 pen, Ifill 84, Bromby 90.
Leicester: Douglas, Maybury, McCarthy, Johansson, Williams, Sylla, Stearman (Gilbert 75), Gudjonsson, Wilcox (Hammond 85), de Vries, Connolly.
Subs Not Used: Dublin, Henderson, Gerrbrand.
Goals: Connolly 50.
Ref: L Mason (Lancashire).