The boyfriend of a woman who was allegedly the victim of a sex attack in Adelaide's parklands has told the District Court that he heard her screams over the phone.

Benjamin Joshua Heldon, 45, is on trial charged with two counts of rape over the alleged attack in Victoria Park in Adelaide's CBD in December 2013.

The court heard the woman was walking to her boyfriend's house at 11:40pm after having drinks with friends at the Kings Head Hotel on King William Street when a man grabbed her and pushed her to the ground.

Her boyfriend, who cannot be identified for legal reasons, told the court on Wednesday he was talking to his girlfriend on the phone when she was attacked.

"I did ask her to get a taxi but unfortunately she said there weren't any around," he said.

"The next thing I heard was 'oh shit,' as if she was startled.

"Then I heard yelling and screaming."

He told the jury he heard the sound of her running and her handbag "jinging" before she yelled that her boyfriend and the police were on their way.

"I could tell that something wasn't right at this point," he said.

The boyfriend said he heard a male's voice but could not make out what the man was saying.

"It was sort of eerie how he wasn't yelling, or anything, but there was something wrong," he said.

The prosecution said the woman fought off her attacker after he sexually assaulted her by using her legs to push him off her body.

The court has heard that during the struggle she also punched the man in the face and pulled out a long dreadlock from his head and that DNA from the dreadlock was matched to Mr Heldon in 2016.

Dreadlocks 'found hanging in accused's bedroom'

Prosecutor Emily Telfer SC said when police located Mr Heldon living in New South Wales they found a bundle of dreadlocks hanging on a hook on his bedroom wall.

The boyfriend told the court that while he and his father searched the area for his girlfriend, his mother called, saying that she had made it back to their house.

"She was clearly distressed," he said.

"She was dishevelled, she was icing her hand, her eyes were a bit red and teary, she had a scratch on her neck and chest."

He said she had "bloodied fingernails" as well as scratches on her hands.

The court heard her boyfriend found her shoes and handbag in the park and police later located her glasses, the dreadlock and a clump of hair on the ground.

The court also heard evidence from a doctor, Greg Dayman, who examined the woman's injuries three days after the attack, and from a crime scene investigator.

The trial continues.