James Baillie (40) had a knife and George Merrilees brandished a baton when they both turned up to rob the 17-year-old at his flat in Burnside Court, Camelon.
They confronted the youth, who cannot be named for legal reasons, but following a struggle he managed to take the knife from Mr Baillie and repeatedly stabbed both men.
The High Court in Edinburgh heard Mr Baillie had earlier won £320 at a bookmakers and used his winnings to purchase a quantity of crack cocaine.
He revealed he had bought the drugs from the youth who was living at the flat in Burnside Court.
He said he was around the youngster was very nervous during the drug deal and described him as having a large quantity of crack.
The court heard an agreement was reached with Mr Merrilees to rob the accused and then split the drugs up afterwards.
Advocate depute Chris McKenna told the court Mr Baillie was under a court curfew at the time requiring him to stay at home until 7am.
He said it was agreed he and Mr Merrilees would attend at the flat where the teenager was living after 7am.
He said: “On June 27, 2019 at about 7am the deceased woke Merrilees. They got dressed and then made their way to the flat, armed with weapons, with a view to carrying out the robbery.
“The deceased was in possession of a large knife in a sheath and a Swiss Army knife and Merrilees had a police style extendable baton.”
Mr McKenna said when they arrived at the unlocked flat there was a struggle in the living room “during the course of which the accused somehow disarmed the deceased by taking his knife from him and repeatedly stabbed both the deceased and Merrilees with the deceased’s knife, causing the death of the deceased and seriously injuring Merrilees”.
The youth began to leave the flat but was stopped by other occupants with one of them asking him: “What have you done?”
The teenager responded: “They tried to rob me.” He was told: “You stabbed him, you murdered a boy. He’s dead.”
The youth was punched and dropped the knife before running out of the flat.
Emergency services were alerted and one witness told police the person who did it was also injured but had left.
He said he was six feet tall and had a London accent.
Mr Merrilees was found to have sustained seven stab wounds and underwent surgery after suffering life-threatening injuries.
Mr Baillie was stabbed four times in the chest area with the most significant wound injuring the left lung and left side of the heart.
Following the fatal assault police went to London as efforts were made to trace the youth.
He handed himself in at Bromley police station on July 15 with a solicitor accompanying him.
The youth admitted culpable homicide by killing Mr Baillie on June 27 this year by repeatedly stabbing him on the body with a knife, when he appeared at the High Court in Edinburgh earlier today.
He also pled guilty to assaulting Mr Merrilees to his severe injury, permanent disfigurement and to the danger of life by repeatedly stabbing him.
The Crown accepted he had acted under provocation.
The court heard the youngster was a first offender who normally resided in London with his mother.
He boarded a train at London’s Kings Cross station on June 23 and travelled to Edinburgh before arriving in Falkirk and meeting up with a man who offered him a place to stay.
Defence counsel Derek Ogg QC said the youth had sustained defensive injuries during the incident at the flat.
The judge, Lord Beckett, deferred sentence for the preparation of a background report on the teenager including a risk assessment and he was remanded in custody.