"He picked up a glass vodka bottle and struck the victim on the back of the head, knocking him unconscious."
While the man lay motionless on the lounge floor, Ralston attempted to flee from the address with his girlfriend.
However, another occupant discovered what had gone on and confronted him.
An altercation took place between them but it was several months before police caught up with Ralston.
As a result of the attack, the victim was cut and bruised, experienced pain in his neck, shoulder and arms and lost a tooth, the court heard.
The defendant pleaded guilty to injuring with intent to do grievous bodily harm and
the judge noted that he had a track record of violence.
But his last indiscretion was seven years ago.
Counsel Ann Leonard said her client had been bedevilled by alcohol problems since he was a teen.
He struggled to express his emotions, had suffered relationship failures and used substances as a crutch, she told the court.
Testament to that were charges of aggravated drink-driving and aggravated driving while disqualified, committed by Ralston in March this year.
Judge Phillips called the attack on the flatmate "extreme violence" and said the man was vulnerable because of his state of intoxication.
Ralston was jailed for two years, eight months and banned from driving for 18 months.