A Corio teenager's avoided jail despite using a knife to scratch a cross into his girlfriend's chest.

19-year-old Aaron Murphy has pleaded guilty to recklessly causing serious injury and unlawful assault over an incident in February in which the victim was also punched, and then forced to clean her own blood off a wall.

According to the Geelong Advertiser Murphy argued the victim had cut herself and he was trying to stop her from committing self-harm.

He's been given a three-month suspended sentence and fined $1,000.

Picture: Aaron Murphy (Geelong Advertiser)