He tried to blame one of his friends for the stabbing but an Old Bailey jury convicted him of murder by a majority of 9-1 and he was sentenced to detention at Her Majesty's Pleasure with a minimum term of ten-and-a-half years.
But Judge Richard Marks QC refused to lift an order banning the identification of the killer after being told he would be appealing his conviction.
The judge said there were 'a number of legal complexities' that are 'likely to be the subject of review'.
He said of Mr Grisales: "No sentence I pass could bring him back or is likely to be regarded by his family as sufficient punishment for what you did."
He told the killer: "Having been handed that knife, you stabbed Steven Grisales through the chest and then ran away, totally indifferent to the fate he had suffered.
"You have continued to deny the offence, seeking to blame a friend of yours for what happened and so have shown no regret or remorse whatsoever for what the jury found you did.
"For one so young you have a bad record."
The teenager waved to the public gallery amid shouts of 'love you' as he was led away to the cells to begin his sentence.
The sentence was reduced from 12 years - the starting point for a juvenile convicted of a knife murder - because of the killers age and because it could not be proved he had taken the knife with him to the scene, the judge added.
The teenager has two convictions for two separate robberies - committed within months of each other - from 2009, including one in which an accomplice was armed with a metal compass.
One another occasion he was caught with a knife at school.
At the time of the killing, he had wrenched of an electronic tag he was required to wear under the terms of a youth rehabilitation order, imposed just weeks earlier for burglary.
Mr Grisales had been living with his father in Argentina but had moved to London weeks earlier in order top begin a three-year architecture scholarship at Westminster University.
On August 31 last year he was making his way along College Close, Edmonton, when he walked past a group of teenager boys and girls in the street.
Although no independent witnesses saw the start of the confrontation, both the 15 year-old and one of his friends admitted they were throwing green spiky horse-chestnuts in the street.
A local resident, Mandy Addy, looked out of her window after hearing shouting and saw Mr Grisales trying to placate one of the teenagers.
She then saw the youth swing his arm at the victim and hit him in the left side of the chest.
Another neighbour, father-of-five Martin Casey, was in his front garden in College Close when he saw two black boys and a girl having an argument with Mr Grisales.
The youths threw punches and kicks at the victim, who dropped his bag and coat before picking up a child's skateboard lying on the pavement.
Holding it over his head, Mr Grisales told the youths: "You think I'm afraid of that, I'm not afraid of that."
He then hit the 15 year-old boy over the head with the skateboard before letting it fall to the ground, the court heard.
Mr Casey said: "That's when [the 15 year-old boy] put his hand in his pocket and pulled out a knife. It looked like a kitchen knife. The blade was about five to six inches."
He then saw the victim being stabbed once in the chest. Mr Grisales collapsed in his garden with blood seeping into his shirt.
The 15 year-old boy was later picked out from CCTV images of the three men by Mr Casey, who also recognised the youth's streetname.
The teenager handed himself in at Edmonton Police station on September 5, 2011, and gave a prepared statement blaming one of his friends.
He claimed that he and one of his friends started 'throwing spiky objects' at two girls they knew.
"We did this recklessly and one of the spiky objects went close to a man who was walking in the street," the statement read.
"This man started shouting and swearing at me. It was aggressive and abusive. He was very angry.
"I was closed to him and the man crossed the road and picked up a skateboard. He hit me on the head twice.
"I punched him in the face. I did so in self defence while I was being attacked."
The teenager said he heard one of the girls telling the third boy to "take the knife."
He continued. "I saw my friend appear to punch [Steven Grisales] in the chest. I saw blood on his t-shirt. I ran away down the close."
His story was supported by his friend who also told the court that he saw the third boy lunge at Mr Grisales.
Jurors also heard from the boy's mother, who claimed that the third boy had confessed he was responsible for the killing.
Michael Bromley-Martin QC, defending, said of the killer: "This young man is not wicked. But he is selfish, he is headstrong and he is violent and he has done a great, great wrong."
He added: "He doesn't understand in the same way as someone older than he the consequences of his actions."
The 15 year-old boy, from Enfield, north London, denied murder.
