The woman, whose name is protected by a publication ban, told a Quebec courtroom about the violent February 2013 encounter that culminated in charges of assault and sexual assault against the now-suspended senator.
She was the star Crown witness on the first day of Brazeau's trial in connection with the incident, which took place at a home in the city of Gatineau, north of Ottawa.
Brazeau, 40, has pleaded not guilty.
Speaking through an interpreter, the woman delivered her testimony just a few metres away from Brazeau, who was kicked out of the Conservative caucus shortly after his arrest.
He gazed at her through much of her testimony, which was at times both explicit and shocking.
WARNING: Graphic content may disturb some readers.
She described how she clung, topless, to a railing inside the residence as Brazeau tried to shove her down a stairwell with his feet. When the thin wooden banister spindles snapped, she tumbled down the flight of stairs.
Moments later, she said she found herself face down across Brazeau's legs at the bottom of the stairs. That's when she alleges he pulled her pants down, breaking the top button, and tried to insert his finger into her rectum.
"It happened so quickly that I found myself in this situation," the woman told the trial, which is being heard by a judge alone.
A short while later, he tried unsuccessfully to assault her a second time in a similar fashion, she alleged.
The physical confrontation occurred in the morning, after a verbal altercation the night before, the woman testified.
The night before, Brazeau had been angry about a TV news report that put him at the centre of a controversy tied to an aboriginal group he used to lead, she testified. He tried to record the report, and grew agitated, nervous and worried, she said.
He was drinking martinis and another cocktail mixed with orange juice as he checked Twitter and sent messages on his smartphone, the woman testified. She said she couldn't tell if he was drunk.
Shortly after the report aired, she said, he told her he had received a Facebook message from an ex-boyfriend of hers — a message telling him to pay back money he allegedly owed the Senate.
At that moment, she said he became "aggressive with a loud tone."
"He approached me like it was my fault," she said.
In an attempt to calm the situation, she left the room. The next morning, she told the court, Brazeau confronted her about the Facebook message once again.
She said he started pushing her before she had a chance to put on a shirt or a bra.
Police photos taken of the complainant the day after the alleged attack showed bruises and red marks on her back, arm, wrist, shoulder and knee.
Gatineau police officer Patrick Quinn also presented photos taken at the residence the day of the incident.
Some of the images showed the broken spindles of railings from different stairways inside the three-storey house.
Police also found a damaged, framed photo featuring three people: the alleged victim, Brazeau and Prime Minister Stephen Harper. Harper's face had been torn out of the photo and then pieced back together.
In addition to the photos, the judge also saw three pieces of evidence that the woman testified belong to her: an animal-print bra with a broken strap, a metal button from a pair of pants and a torn shirt.
Quinn testified it appeared like an altercation "with a certain amount of violence" had taken place in the house.
Proceedings were briefly halted Monday when the Crown asked Judge Valmont Beaulieu to have the media and public excluded from the courtroom during her testimony. Beaulieu denied the request after a short recess.
The woman is scheduled to be back on the stand Tuesday. The Crown expects the trial to last three days and plans to call more police witnesses to testify.
Brazeau was named to the Senate by Prime Minister Stephen Harper in 2008.
Days after Brazeau was kicked out of the Conservative caucus, he was forced to take a leave from the Senate and was later suspended.
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