Manchester United were left shell shocked as Leicester produced a stunning comeback to beat the Red Devils.
It all looked so good for United when Ander Herrera put them 3-1 up with just over half an hour to play, but the game turned on a hugely contentious penalty decision which referee Mark Clattenberg may not want to see again.
That decision acted as the catalyst as the home side scored four times in 20 minutes to claim all three points.
It was United who made the early running as they took the lead after 13 minutes.
Robin van Persie had already been denied once by Kasper Schmeichel, but the Leicester keeper could do nothing about the header van Persie produced from a fine cross by Radamel Falcao.
Things got even better for Louis van Gaal's side as the doubled their lead with a magnificent goal.
Angel Di Maria exchanged passes with Wayne a Rooney before scooping a fantastic finish over Schmeichel from just inside the area.
United's two goal advantage was short lived as Ulloa scored almost immediately with a fine header from a Vardy cross, although the ball looked like it may have gone out of play before the cross was made.
Van Gaal's injury woes continued as he saw Jonny Evans go off injured inside the first half an hour, with Chris Smalling coming on to replace him.
Rojo headed a Di Maria corner over just before the break whilst Falcao came within a whisker of his first United goal as his effort rebounded back off the bar with Schmeichel beaten.
United, though, weren't to be denied and Ander Herrera was on the right spot to finish with a clever back heel from Di Maria's initial effort.
It could already have been worse for Leicester with Richie De Laet fortunate not be sent for an early bath as he was tormented at times by the speed and trickery of Di Maria.
United looked likely to add to their rally until Clattenberg stepped in to completely change the complexion of the game.
Rafael looked as if he had been fouled by Vardy, but the referee played on and moments later pointed to the penalty spot as Vardy went to ground.
It was, at best, a very soft award with United players perplexed by the referee's decision, especially as there was far less contact than Vardy's earlier shove on Rafael.
Having been given the opportunity David Nugent made no mistake from the spot and the Foxes were level just two minutes later as they punished United for their failure to clear.
Esteban Cambiasso struck low and hard past de Gea as the ball ping-pinged in and around the United area to make it 3-3.
The double whammy seemed to shock United and it was the home side who now looked the most likely to add to their tally.
And add to it they did as United were guilty of more reckless defending to gift the Leicester the advantage.
Mata lost possession in the Leicester half and there was nobody at home at the back for United as De Laet found Vardy in acres of space to coolly slot past de Gea.
United's capitulation was complete with seven minutes remaining as Vardy won a second penalty, this time being brought down by Blackett.
The United youngster saw red for denying the Leicester striker a goalscoring opportunity and Ulloa converted from the spot to make it 5-3.
There was no way back for United, but van Gaal and his side will no doubt rue their luck and the unfortunate twist of fate that cost them from the hand of referee Clattenberg.
Written by Andrew
It all looked so good for United when Ander Herrera put them 3-1 up with just over half an hour to play, but the game turned on a hugely contentious penalty decision which referee Mark Clattenberg may not want to see again.
That decision acted as the catalyst as the home side scored four times in 20 minutes to claim all three points.
It was United who made the early running as they took the lead after 13 minutes.
Robin van Persie had already been denied once by Kasper Schmeichel, but the Leicester keeper could do nothing about the header van Persie produced from a fine cross by Radamel Falcao.
Things got even better for Louis van Gaal's side as the doubled their lead with a magnificent goal.
Angel Di Maria exchanged passes with Wayne a Rooney before scooping a fantastic finish over Schmeichel from just inside the area.
United's two goal advantage was short lived as Ulloa scored almost immediately with a fine header from a Vardy cross, although the ball looked like it may have gone out of play before the cross was made.
Van Gaal's injury woes continued as he saw Jonny Evans go off injured inside the first half an hour, with Chris Smalling coming on to replace him.
Rojo headed a Di Maria corner over just before the break whilst Falcao came within a whisker of his first United goal as his effort rebounded back off the bar with Schmeichel beaten.
United, though, weren't to be denied and Ander Herrera was on the right spot to finish with a clever back heel from Di Maria's initial effort.
It could already have been worse for Leicester with Richie De Laet fortunate not be sent for an early bath as he was tormented at times by the speed and trickery of Di Maria.
United looked likely to add to their rally until Clattenberg stepped in to completely change the complexion of the game.
Rafael looked as if he had been fouled by Vardy, but the referee played on and moments later pointed to the penalty spot as Vardy went to ground.
It was, at best, a very soft award with United players perplexed by the referee's decision, especially as there was far less contact than Vardy's earlier shove on Rafael.
Having been given the opportunity David Nugent made no mistake from the spot and the Foxes were level just two minutes later as they punished United for their failure to clear.
Esteban Cambiasso struck low and hard past de Gea as the ball ping-pinged in and around the United area to make it 3-3.
The double whammy seemed to shock United and it was the home side who now looked the most likely to add to their tally.
And add to it they did as United were guilty of more reckless defending to gift the Leicester the advantage.
Mata lost possession in the Leicester half and there was nobody at home at the back for United as De Laet found Vardy in acres of space to coolly slot past de Gea.
United's capitulation was complete with seven minutes remaining as Vardy won a second penalty, this time being brought down by Blackett.
The United youngster saw red for denying the Leicester striker a goalscoring opportunity and Ulloa converted from the spot to make it 5-3.
There was no way back for United, but van Gaal and his side will no doubt rue their luck and the unfortunate twist of fate that cost them from the hand of referee Clattenberg.
Written by Andrew