Dale Gardiner, 25, attacked William Wardrop after visiting his home in Larkhall, South Lanarkshire.
Paramedics fought for 40 minutes to save the 23-year-old, but he died in the hospital.
Gardiner will be sentenced next month after being found guilty of culpable homicide under provocation.
During the incident, which occurred in the early hours of May 22, 2020, the killer claimed he was acting in self-defense.
Prosecutors insisted that what he did was “not a proportionate response.”
Gardiner had been charged with murder before being convicted of the lesser charge.
The men had been together at Gardiner’s then-home on Riverside Road, where they played video games, according to the High Court in Glasgow.
Before the pair got into a fight, another man there said things were “friendly enough.”
Despite the fact that the argument had calmed down at one point, the victim was fatally stabbed.
Mr Wardrop staggered away for a moment before collapsing.
Gardiner was described as “hysterical” and crying after the attack about his “best friend.”
“He ran at me, and I stabbed him,” he said at one point, adding, “Is he all right, my pal Willie?”
Prosecutor Stewart Ronnie stated to jurors, “It is also clear Dale Gardiner was telling anyone who asked what had happened.”
According to Mr Ronnie, the killer “targeted William’s chest with a lethal weapon.”
“I suggest his actions could not be considered proportionate,” the advocate depute said.
Lady Rae postponed sentencing to await reports.
“William was a much-loved dad, brother, and fiancé who will be sadly missed by us all,” his family said in a statement issued by Police Scotland at the time of his murder.
“He will live on in our hearts forever.”