Ms Huth sued him in 2014 and is seeking unspecified damages for sexual battery and emotional distress in a civil trial in California.
The actor, 84, denies the allegations.
Donna Samuelson, who was Ms Huth's best friend and 17 at the time, told the court she saw her crying and in deep distress minutes after the alleged incident.
Ms Samuelson, now 64, said: "She said 'I want to go, I wanna leave,' she was crying."
She said she initially felt angry because she had been looking forward to spending the rest of the afternoon and evening at the mansion, but then Ms Huth explained herself. A civil trial against the actor Bill Cosby over allegations he assaulted a teenager at the Playboy Mansion in the 1970s is due to start today, less than a year after he was released from jail.
This story is out of date - go here to read about the best friend of Cosby's accuser saying the teenager was left "crying" after alleged assault.
Judy Huth, now 62, alleges the actor made her drink beer and molested her on a bed in 1974 when she was 15.
She claims Cosby, now 84, who is not planning to attend the hearing in California, invited her and a friend to the Los Angeles mansion the week after meeting them on a film set at a park.
There, she alleges, he forced her to perform a sex act.
Ms Huth sued Cosby in 2014 and is seeking unspecified damages for sexual battery and emotional distress.
He denies the allegations.
The84-year-old actor and comedian was sentenced to three to 10 years in prison in2018 following his conviction on three counts of aggravated indecent assault.
It had been alleged that Andrea Constand, a former employee of his alma mater Temple University, was drugged and molested at Cosby's home in 2004.
But last year the Pennsylvania Supreme Court threw out his conviction, saying the prosecutor who brought the case was bound by his predecessor's agreement not to charge Cosby.
Cosby was previously known for his role as the lovable husband and father in the classic1980s television comedy series The Cosby Show.
However, his family-friendly reputation was shattered after more than 50 women accused him of sexual assaults, which they said took place over nearly five decades.
Ms Constand's allegations were the only ones against Cosby that were not too old to prevent criminal charges being brought, as the US has a principle called theStatute of Limitations, which requires criminal proceedings to be started within a specific period.
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