Jameis Winston's Friends -- We Watched Her Perform Oral Sex On Him ... She Was 'More Than Willing'

One of the men who was with Jameis Winston on the night of the alleged rape told police he WITNESSED the accuser perform oral sex on the Florida State QB ... and she seemed "more than willing."

TMZ Sports obtained documents which show that Jameis' pal Chris Casher told police he went to Potbelly's bar with JW and another friend, Ron Darby, on the night of the alleged rape.

Casher says the accuser, a blonde woman, was not drunk when she left the bar with Jameis and when they got to his apartment, they went into JW's bedroom together.

Chris says, "Since the door was partially open, I looked through the opening and we could see her giving Jameis oral sex. They had only been in the room a few minutes before I witnessed her giving him oral sex."

"Jameis was facing the door with his hands on his hips while she was in front of him on her knees. I witnessed them both take each other's clothes off and lay on the bed."

"Jameis and the blonde female began having intercourse."

Chris says .. "as a joke" he busted into the room to embarrass Jameis ... but the woman shooed him out of the room, closed the door and turned off the lights for more privacy.

Chris says he and his other buddy Ron could hear the two having sex.