A man who admitted trying to strangle his girlfriend has been jailed for six years at Lincoln Crown Court.
Kevin Roberts throttled Amanda Jones until she began to turn blue.
But she was saved when a teenage boy intervened.
Even after the lad called police Roberts resumed his attack on his victim only stopping after he was knocked out.
Roberts ,52, of Bramley Close, Louth, admitted a charge of attempting to cause grievous bodily harm on 2 September 2012.
Judge Michael Heath told him “This was a sustained attack. You throttled her. If it had not been for the boy, whose courageous intervention does him enormous credit, the strong likelihood is that you would have killed that lady. “
Stephen Lowne, prosecuting, said that Roberts had been out for the evening with Ms Jones but went back alone to her home.
He was asleep on the sofa when she returned.
Amanda Jones went to bed herself but during the night Roberts burst into her room.
“She remembers him placing his hands around her neck and starting to throttle her. After that point she remembers very little.”
Mr Lowne said that Roberts began to strangle Ms Jones and during the attack began shouting that she was going to kill her before the boy intervened.
Mr Lowne said: “At first he tried to prise Roberts off Amanda Jones. She was turning blue.
“The boy started to punch Roberts to the head. He punched him but it was not having any effect. Then he grabbed a bedside table lamp and started to strike the defendant about the head.”
Roberts released his grip on Ms Jones and lapsed into unconsciousness but later came round and resumed the attack.
“The boy picked up a glass candlestick and hit the defendant over the head with that. Eventually Roberts entered into unconsciousness.”
Police arrived in response to the boy’s 999 call and Roberts was arrested. He later told officers he had little recollection of the incident.
The court was told that the woman was left severely affected by the attack.
Mr Lowne said: “She has had to leave the house where she lived because she cannot face going back there. She describes herself as a a shadow of her former self.”
David Eager, defending, said Roberts had never been in trouble before and simply “flipped”.
“He is a man of good character who has led a blameless existence. On this night for some reason he lost the plot.”
At the end of the case Judge Heath praised the boy for his “courageous” intervention and directed the High Sheriff of Lincolnshire to award him £500 as an appreciation of what he did.