The man was sat with his wife as Dr Ong entered the room and led her away for a sex session.
The doctor stripped with a stethoscope in one hand
Later, the mother detailed the incident in her diary as she wrote "what a great buzz".
The woman told a Medical Council that she made appointments for intercourse with the doctor and enjoyed weekly liaisons with him at her home in a seven-month affair.
The GP stripped off with his stethoscope in one hand while he undressed with the other as they jumped into bed on one visit to her house, she told the hearing.
Giving evidence in private, screened from the press and public, the married woman, known as Patient A, recalled how the sexual contact began during a consultation at the XXXX Group in September 2008.
She said she had endured a "bad year" and had no sex drive which she described as like "being dead from the neck down". Dr Ong later told her "maybe she was with the wrong person".
Her husband had also found out something embarrassing about her past and she had previously tried to commit suicide.
She admitted feeling vulnerable after having a few lunchtime drinks with her sister before seeing Dr Ong about a lump on her stomach.
"He examined me and then he just his put his hands further down. He put them down to my vagina and underneath my clothing," she said.
Patient A said she was shocked and laughed nervously as she told him: "I think my husband should do that".
Dr Ong then pulled her to the examination table, she unzipped his trousers and then masturbated him and gave him oral sex, the panel was told.
He called her the next day and asked if "the coast was clear" before he drove to her home, walked in and locked the door. He then went into the bedroom and started stripping off as she sat dressed on the edge of her four-poster bed.
The woman said: "I told him it was my house and if he was stripping then I should have the privilege of telling him when to strip."
They went on to have oral sex and full intercourse before she said Dr Ong delivered an "awful lecture" in which he said no-one at the practice needed to know about their affair.
The pair would go on to meet every Tuesday on her day off from work.
She recalled another home visit in which he stripped off when arriving.
"He had his stethoscope on my chest in one hand and he was getting his kit off with the other. We just jumped into bed and had sex," she said.
Regular visits to the surgery would also be arranged with Patient A particularly keen to grab the last appointment on Fridays as Dr Ong was "always running late" and it would be "awkward" with other patients in the waiting room.
Throughout the affair the mother kept a diary - she would draw smiley faces on dates where she had met the doctor and would write M in an inner circle, meaning he was "great in bed".
On October 20 she wrote "what a buzz" after her sexual liaison with the doctor while her husband sat yards away outside the door.
She told the panel: "That was the day when I referred to my husband, I was really angry at the time.
"The bleeper was not working to call you into the doctor's room so he (Dr Ong) had to come through."
She added: "Dr Ong was not happy because he asked who I was talking to. I told him it was my husband and he nearly fell off the couch."
In February 2009 she said Dr Ong visited her in hospital while his wife was also there recovering from an operation.
"He said he could kill two birds with one stone," she said.
"Did he?" asked the Medical Council counsel.
"Yes, while his wife was in the theatre," she replied.
She said the relationship ended when Dr Ong was suspended from duty and she later gave a witness statement to the MC in which she felt pressurised to do so but also "morally obliged".
Patient A explained: "It was the way our relationship started that was wrong. I felt I had to do it, I did not want to do it."
She said she thought the affair started because she believed Dr Ong was "very unhappy" and was not "getting sex at home".
Asked about the consequences of the affair, she said: "Disastrous, totally disastrous. I'm emotionally lost.
"My husband is divorcing me, my daughter is not speaking to me. It could not get any worse."
