Accused killer trying to 'save girlfriend'

A man accused of murdering his pregnant girlfriend in Sydney was a zealous father who was simply trying to save his unborn child from her ice addiction, his barrister says.

Christopher John Anderson has pleaded not guilty to murdering Allira Green who died from a single stab wound to her chest in the early hours of August 3, 2013. She was five months pregnant.

On the opening of his trial on Monday, the Supreme Court heard the pair had a volatile relationship, with Ms Green contacting police twice in June 2013 to report domestic disturbances.

Crown prosecutor Virginia Lydiard said this relationship upheaval was illustrated in a series of texts sent between Ms Green and Anderson in the days leading up to her death.

Then in the early hours of August 3, Anderson arrived at the Maroubra unit in Sydney's east where Ms Green and two other women, Allira Holt and Louise Bodeker, were.

Ms Holt said Anderson looked "scary and full of rage" and that Ms Green told him to "get out and no one wanted him there", Ms Lydiard said.

A scuffle ensued with Anderson allegedly grabbing Ms Holt by the throat, pushing her and then punching her to the face four to five times.

During this struggle Ms Green was seen grabbing a knife from the kitchen before Anderson allegedly threatened to hurt her.

The 23-year-old hit the floor and died shortly after.

Meanwhile Anderson - then 39 - fled and called a friend, saying he had been set up and that he was on Xanax and "ice".

He handed himself into police later that day.

Ms Lydiard said the crown would rely on a number of pieces of circumstantial evidence that would prove their case, including the depth of the stab wound, the heated text messages between the pair and that he changed his clothes after the stabbing.

But Anderson's barrister Charles Waterstreet said his client was acting in self-defence and that Ms Green was an "angry woman", who was high on drugs and had launched herself at him with a knife.

Anderson, he told the jury had been "zealous" in the lead-up to the killing as he was trying to protect his baby and rescue Ms Green from her addiction to ice.

The trial continues.