Ms Denham said she came home to find Clague packing his truck with camping gear for the weekend after an earlier row.
She began unpacking the vehicle and the pair met in the doorway of the garage where the alleged altercation developed.
Ms Denham told the jury Clague grabbed her from behind, shook her so hard she felt like she was "in a car crash" and then pushed her hard onto some steps.
She fell on her tail bone.
"I jumped up immediately even though my back was in an incredible amount of pain," Ms Denham said.
"I didn't know what was coming next. He just stood there with his fists clenched. It was like white rage... I've heard it called. He didn't look like Peter."
She said she looked for something with which to defend herself but could find nothing so told him: "your career is over".
"It had an instant reaction. He stopped in his tracks," Ms Denham told the court.
Clague's lawyer Michael Lloyd said his client had only grabbed his former partner "in a pleading way" and a slip on the polished floor had caused him to overbalance and push Ms Denham backwards on to the step.
"His defence has always been that it was in the context of Ms Denham absolutely going off her rocker, being loud, hurling expletives of abuse within earshot of the neighbours and the child," he said.
Ms Denham accepted she had hired Carrick Graham as a public relations consultant who put out a press release regarding the case, after police decided not to charge the former executive principal of Kristin School.
Mr Lloyd said it sparked one of several media campaigns against Clague and he told the jury she was out to destroy the man with whom she was in a relationship for six years.
She also wrote a letter to Green MP Catherine Delahunty which began: "I was in an abusive relationship with a high-profile man?"
"She has actually developed over the years this persona of a victim of domestic violence that's completely fictional," Mr Lloyd said.
Ms Denham said she was the victim of a psychologically-abusive "tyrant" but defence counsel read several texts in court in which she called him "sexy man" and "darling one".
The complainant explained she was only telling him what he wanted to hear.
The trial before Judge David McNaughton and a jury of seven men and five women is expected to finish before the end of the week.
