Ex-Michigan State basketball star Mateen Cleaves says he DID have sex with the woman accusing him of rape ... but he's adamant the encounter was 100% consensual.
The 41-year-old -- who was the 14th overall pick in the 2000 NBA Draft -- appeared in court in Flint, Michigan for opening statements in his trial ... where he is facing multiple felony charges.
As we previously reported, the accuser claims Cleaves took her to a motel in 2015 and held her there against her will. She claims Cleaves forced himself on her and raped her.
The woman told officials she managed to escape from the motel room and got help from someone nearby.
But, during Thursday's hearing, Mateen's attorney told the 14 people in the jury box that the woman is distorting the truth ... claiming her decision to have sex was "of her own free will."
The attorney suggested she had regretted her decision after the fact -- but told the jury, "Regret is not rape."
"By the time the truth comes out, the truth will set my client free," the attorney said according to DetroitNews.com ... "The truth will be there; the truth will be self-evident."
Prosecutors are painting a different picture ... acknowledging the woman voluntarily went to the motel with Cleaves following a golf tournament where they had met hours before ... but claim she made it VERY clear she did not want to have sex.
Cleaves is facing unlawful imprisonment, assault with intent to commit criminal sexual penetration, 2nd-degree criminal sexual conduct and 2 counts of 3rd-degree criminal sexual conduct. He faces up to 15 years in prison if convicted on all charges.