A man felt something was amiss when his girlfriend, who had earlier been exchanging text messages with him while she was out clubbing with co-workers, went silent.

He used the Find My iPhone app to track her down to a house in Hume Heights, Bukit Timah, and found her in a stupor, lying on a mattress with another man.

Yesterday, that man - Ong Soon Heng - went on trial for abducting and raping the woman in the early hours of July 24, 2014.

Ong, 40, and the woman, who is 15 years his junior, were at Zouk with their respective friends when he plied her with drinks, the High Court heard. The woman, then a 22-year-old undergraduate, was an intern at a food and beverage company and Ong, a friend of her employers, was a frequent visitor.

Deputy Public Prosecutor Sellakumaran told the court that Ong, who was divorced, was interested in her but she did not reciprocate his feelings as she was in a long-term relationship. However, she tolerated his advances in order not to jeopardise her internship, he said.

Surveillance footage showed that at about 4am on July 24, 2104, Ong hauled her limp body over his shoulder and placed her in the back seat of his car before driving home. He allegedly raped her at his home while she was unconscious.

One of her friends, a 23-year-old undergraduate, testified yesterday that Ong and the woman were kissing "mouth to mouth" in the club, but she found it "weird" as the woman was attached.

She said that during the kiss, the alleged victim was "standing up but wasn't very stable".

She said that when Ong said he would drive the unconscious woman home, she "trusted him and took his word for it". She assumed Ong knew where the woman lived.

She disagreed when Ong's lawyer, Mr Peter Fernando, contended that his client did not ply the woman with drinks.

DPP Sellakumaran told the court the woman's boyfriend will testify how he had difficulty rousing her after he found her in a pair of boxer shorts and T-shirt which did not belong to her.

He will also testify that Ong's first reaction was to deny he had done anything with her.

Details have yet to emerge on how the boyfriend managed to enter the property, which is believed to be a "black and white house".

The victim was disoriented and drifting in and out of consciousness even as she underwent a medical examination later that day, added the DPP.

She was found with 62mg of alcohol per 100ml of blood at 12.45pm. A medical report estimated her blood alcohol concentration was between 210.50mg and 254.50mg per 100ml of blood.

The report said she was severely intoxicated and was "highly unlikely" to have had consensual sex at the time. The prosecution will also produce an audio recording of Ong admitting to the woman's father that he had sex with her.

The maximum punishment for rape is 20 years in jail and caning or a fine. The maximum punishment for abduction is seven years in jail and caning and a fine.

The trial continues.