NORRISTOWN, Pa. — Bill Cosby was supposed to be her mentor, Andrea Constand told a jury here Friday. But instead he became her attacker, she said, so unrelenting in his sexual pursuit — even after she had rejected his advances — that he drugged and molested her during a visit to his home in January 2004.

“I was kind of jolted awake and felt Mr. Cosby on the couch beside me, behind me, and my vagina was being penetrated quite forcefully, and I felt my breast being touched,” Ms. Constand said. “I was limp, and I could not fight him off.”

Ms. Constand was more composed and less emotional in giving her account on Friday than she had been last summer, when she first testified about her encounter with Mr. Cosby at his house near Philadelphia.

A mistrial was declared in that first sexual assault case when the jury became deadlocked. This time, Mr. Cosby’s defense team has taken a more aggressive stance toward Ms. Constand, describing her as a “con artist” who engaged in a consensual encounter and then concocted a story of assault to score a big payday.