The woman, whose name is protected by court order, was at North York General Hospital in November, 2009 for a knee replacement.
George Doodnaught, her anesthesiologist, is charged with 21 counts of sexual assault. He has pleaded not guilty to all of charges against him.
The 64-year-old doctor had worked as an anesthesiologist at the hospital from 1981 until his arrest in 2010.
The prosecution alleges that Doodnaught assaulted 20 of the women at the hospital. Another woman was allegedly assaulted at a private clinic.
The 57-year-old woman who testified on Wednesday told the court she remembers coming to during surgery, in a panic.
"I feel my hand enclosed around something," she said. "I try to move my hand but I can't ... I hear a voice over and over again saying 'No, no, no, you're doing great.' Soothing words."
The woman told the court she became aware that she was feeling a man's penis in her hand.
"I realize the object in my hand is getting larger and I realize what it is. I am overwhelmed by how I am a strong person, yet I can't get out of this," she told the court.
She testified the voice kept speaking, getting more excited, and though her eyes were closed she knew it was Doodnaught, whom she had spoken to right before her surgery.
Many of the alleged victims have testified about similar — though not identical — assaults inside the operating room.
Some testified they complained to hospital staff immediately. Others, like the woman who testified on Wednesday, only came forward after the first criminal charges were laid in March 2010.
The woman testified she told her daughters what happened right after the surgery.
She said they looked horrified and didn't seem to believe her. She decided not to tell anyone at the hospital.
"I knew in my heart it occurred. I just thought I'm not going to keep talking about it if no one believes me, so I stopped," she said.
Under cross-examination defence lawyer Brian Greenspan asked about a visit from Doodnaught the day after her surgery, where he expressed an interest in meeting the woman's boyfriend.
She testified she couldn't believe Doodnaught would have the nerve to visit after what happened.
"So that visit from Dr. Doodnaught made you question whether the incident had actually occurred?"
"Correct." the witness responded.
The complainants — who range in age from 25 to 75 — allege that Doodnaught assaulted them while they were on the operating table, with other doctors and nurses inside the operating room blocked from seeing what he was doing because of a 'sterile screen.'
The screen is a 1-by-1.5 metre curtain that separates the sterile and non-sterile parts to the operating room.
The trial continues.