Christopher John Barry (53) also known as Jack, was stabbed at his home in Edmonton, north London, in December after he was said to have been involved in an incident with a group trying to get into a party at another address in the block of flats.
A 13-year-old boy was arrested days after the killing, the result of a "verbal altercation" with a group youngsters. The child, who cannot be named for legal reasons, admitted stabbing 53-year-old in court today.
Mr Barry is believed to have been involved in an argument with a group of boys as he attempted to gain entry to the flats in The Broadway. He was followed into the building by two of the boys and stabbed, police said.
Ambulance crews attended but he was pronounced dead at the scene shortly before 8.40pm on Sunday, December 14.
Detective Chief Inspector Neale Baldock, of the Homicide and Major Crime Command, who led the investigation, said at the time: "Our initial inquiries have established that there was a supervised party taking place at another address within the block and the group of males were trying to gain access to this.
"The victim and this group were not known to each other - what started as a minor verbal altercation has escalated into a shocking act of violence."
The defendant's parents as well as relatives of Mr Barry, who was known as Jack and was originally from Cobh, Co Cork, all attended the Old Bailey for the five-minute hearing today.
After being brought into the dock from custody, the boy spoke to his father briefly before the charge was put to him by the court clerk. When asked to confirm his name, the boy replied: "Erm ... yes." His guilty plea to a single count of murder was almost inaudible.
Dressed in a light blue shirt and grey school regulation-style trousers, he was remanded into youth custody by judge Anthony Morris.
The judge ordered a pre-sentence report ahead of sentencing on April 10.