It is the same method he is said to have used in the alleged 2004 attack on Andrea Constand he is on trial for.

Mr Cosby, 79, denies the charge. His lawyer says she agreed to sex and has changed her story to investigators.

Dozens of women say Mr Cosby assaulted them, but statutes of limitation rules mean he is on trial for only one allegation.

In both incidents Mr Cosby is said to have invited a young woman to his home for career advice before offering her a pill to "relax" her and abusing her once she was incapacitated.

Witness Kelly Johnson said she initially hid the pill under her tongue but Mr Cosby then checked to see if she had swallowed it.

She later woke up partially clothed in Mr Cosby's bed with Mr Cosby behind her, grunting, before he forced her to touch his genitals, she told the court.

"I was trying to say something," she said. "I don't know if I was actually speaking."

The case is seen as the biggest US celebrity court case since the murder trial of former American football player OJ Simpson in 1995.

It revolved around "trust, betrayal and the inability to consent", prosecutors told the court in Pennsylvania.

Prosecutor Kristen Feden told jurors that the defendant had "used his power and his fame and his previously practised method of placing a young, trusting woman in an incapacitated state so he could sexually pleasure himself".

As Mr Cosby sat a few feet away, the prosecutor urged jurors to look beyond his father role on the hit 1984-1992 television sitcom The Cosby Show.

That wholesome TV image would be "shattered", she said, accusing the entertainer of "heinous crimes".

Defence lawyer Brian McMonagle countered that Mr Cosby was the victim of false accusations.

"Today I get a chance, with your help, to right a wrong," he told jurors. "I get a chance, with your help, to protect a man from the destruction of the rest of his life."