A man on trial for killing his former lover allegedly followed her into her Sydney unit and stabbed her to death, a court has heard.

Rachelle Yeo “basically lost all her blood” in her Sydney unit from stab wounds inflicted by her former lover, a court has heard.

The gruesome details emerged on the opening day of a murder trial with Paul Darren Mulvihill accused of following Ms Yeo into her Sydney unit and stabbing her to death in July, 2012.

Emergency services tried to revive Ms Yeo.

“They will say they realised from the amount of blood in the unit, it was inconsistent with life,” crown prosecutor Maria Cinque told a Supreme Court jury in Sydney.

“She basically lost all her blood.”

Mulvihill allegedly inflicted the injuries on Ms Yeo with a 21-centimetre knife, which was missing from her kitchen. He has pleaded not guilty to murder.

The Supreme Court heard on Wednesday that Ms Yeo suffered a stab wound to her chest that penetrated 18 centimetres.

Ms Cinque told the court Ms Yeo also sustained another stab wound to her neck.

Mulvihill’s defence barrister Kate Traill said it was a tragedy of Shakespearean proportions.

But Mulvihill did not intend to kill Ms Yeo, she claimed.

“Paul Mulvihill was attacked with the knife by Rachelle Yeo,” she told the court.

“He did what he thought necessary to defend himself.”

The killing followed an affair between Mulvihill and Ms Yeo, who worked together for Sanofi Aventis pharmaceuticals in Brisbane.

Mulvihill had cheated on his wife of 16 years and mother to his children while Ms Yeo had betrayed her fiance and partner of five years.

The affair, which started in mid-2011, began to fall apart when Mulvihill’s wife discovered text messages on her husband’s phone.

Despite Mulvihill’s commitment to counselling with his wife, the affair continued, the court heard.

Ms Yeo accepted a job promotion in Sydney in April 2012.

Ms Cinque said Ms Yeo was obviously starting to lose interest.

Mulvihill was devastated by Ms Yeo’s decision to move to Sydney and cut ties with him, Ms Cinque said.

“He was unable to accept that in reality the relationship was well and truly over.”

The Crown alleges on July 16, 2012, Mulvihill flew to Sydney and went to Ms Yeo’s home on Sydney’s northern beaches and followed her into her unit.

Ms Cinque said one neighbour heard a woman screaming: “oh God, oh God, oh God” and a blood curdling scream.

The court heard police found blood on the walls, in the living room and kitchen and at the door.

Outside the unit, police found a white plastic chain with Ms Yeo’s blood on it.

Ms Cinque said Mulvihill’s wife had found a receipt for a hooded jumper and the plastic chain in his bag before he left for Sydney.

Mulvihill allegedly used a workmate’s credit card to buy a flight from Newcastle to Brisbane after July 16 and boarded the plane under the workmate’s name.

However, Australian Federal Police officers met him at Brisbane airport.

The trial continues.