Dean Kerrie, who was 17 at the time, said Mr Power had entered his home after 3am and attacked him and his mother.
The jury of seven women and four men took just under six hours to come to their verdict following the trial of Dean Kerrie (21), who denied murdering Jack Power.
The accused, who was 17 at the time, said Mr Power had entered his home after 3am and attacked him and his mother.
Following the verdict, Mr Justice Paul McDermott refused to allow Kerrie to remain on bail and remanded him in custody until a sentencing hearing on October 19.
The judge ordered a probation report and a victim impact statement from the deceased man's family.
Following the verdict Kerrie hugged members of his family while the deceased's family and supporters comforted one another at the back of the court.
This was the second time in less than six months that Kerrie went on trial for the same offence. His first trial ended last February when the jury could not agree on a verdict.
In that trial Kerrie took the stand, telling the jury that Mr Power had lost his footing and fell onto a knife that Kerrie had picked up while the deceased was attacking his mother.
He did not give evidence at his second trial but the jury heard that after he was arrested Kerrie told Sgt Pat Kenny: "He should not have come into my house. I was asleep. I heard a smash and the front window breaking.
"Jack was in the hall and grabbed my mother. He started punching and swinging kicks. I grabbed a knife that was next to bed. Stabbed him with it."
Sgt Kenny said Kerrie was holding a bottle of holy water as he spoke.
Kerrie (21) with an address at St Brigid's Square, Portarlington, Co Laois, had pleaded not guilty to murdering 25-year-old Jack Power at Shanakiel, Dunmore East, Co Waterford, on July 26, 2018.
The trial heard that Mr Power had been drinking with friends in a local pub and when he left the pub he saw damage to the wing mirror of his car and believed Kerrie was responsible.
He drove to an area close to where Kerrie lived, picked up a rock and used it to smash one of the front windows of Kerrie's house.
There were differing accounts of what happened next.
The jury heard a 999 call made by Kerrie at 3.44am on July 26, in which the teenager said that Mr Power had come "in the front door at him" and tried to hit him. He said he had stabbed Mr Power in the chest with a kitchen knife but that he didn't mean to.
The deceased's best friend Christopher Lee said he saw Mr Power going into the garden of the Kerrie house. "I saw Dean Kerrie's mother coming towards Jack in the garden and Jack pushed her back and she fell over," said Mr Lee.
Mr Lee said he saw Kerrie in the garden, that he came out towards Jack, turned around and went into the house. "Jack went into the house after him," he added.
Mr Lee went "close enough to the front door" of the house where he saw Mr Power and Kerrie in the middle bedroom through the window. "I saw pushing in the bedroom, Jack pushing Dean," he said.
The witness said he thought Kerrie had left the bedroom first followed by Jack and that they went into the hallway.
"There was a bit of pushing in the hallway. Jack was only a couple of feet away from me. I saw Dean coming from the kitchen with a knife in his hand. Jack was walking out of the house facing me," he continued.
Mr Lee said the accused shouted something at Jack. He added: "Jack was nearly at the front door. Jack turned around and I noticed Dean moving fast and saw a knife in his hand. I saw Dean push his hand towards Jack's chest. Jack was only after turning around and this happened straight away," he said.
Mr Lee said that Mr Power turned and held his chest. "I was standing at the door. I was shouting at Jack, I knew what was after happening. I was in shock. I couldn't believe it," he said.
Kerrie's best friend Dylan Jones was called by the defence and gave a different account. He told defence counsel Ciaran O'Loughlin SC that he was staying the night at the Kerrie home when he was awoken by the sound of glass smashing.
Kerrie got up first, he said, and went to his brother's room. When the witness got up he said he saw a man he now knows to be Jack Power enter through the front door.
"He appeared to be drunk, he was kind of stumbling," he said. "He approached and pushed me against the wall and went into the bedroom and grabbed Dean."
Mr Jones recalled seeing Mr Power "choking" Kerrie and saying: "I'm going to kill you." Kerrie, he said, was screaming, "please get off me," and Mr Jones said he told Mr Power: "Please get off him, he is only a child, leave him alone."
He added: "I thought he was gong to kill Dean."
Kerrie's mother, Ann Fitzgerald, was in the hallway next to the bedroom door when Mr Power grabbed her by the hair and "swung her side to side", he said.
At this point, he said Mr Power stumbled backwards and then into the hallway and out the front door. Mr Jones said he didn't see a knife and didn't see Mr Power being stabbed but he accepted that it must have happened just before Mr Power stumbled backwards. He recalled Kerrie saying: "I think I stabbed him, I need to call the guards." Kerrie was "crying, in hysterics," he said.