She tried to apply an armlock which could have broken her attacker's arm, but he wriggled free and punched her in the face again and again.
She said: 'I was stunned for a moment. Again I could feel him grabbing me and pulling at my clothes.
'My legs were free so I lifted my left leg up on to his shoulder and around the back of his neck. I crossed my right leg over and squeezed together as hard as I could.
'He seemed to struggle for air - which was the point. His head was locked down. He lifted his right hand and pounded as hard as he could on the side of my face.
'I closed my eyes and held it for as long as I could hoping he would pass out in a few seconds. Then I felt his body go limp. I flipped him off, rolled over and crawled through the bushes to the door of the house.'
She later heard him run away and the sound of a car starting.
Willis, of Churchdown, Gloucester, admitted assault causing actual bodily harm but denied sexual assault, claiming he had confronted her because he saw her take a photo of him when he was urinating in a driveway.
But DNA from his hands was found on her shorts and after his arrest she picked him out in an identification procedure.
A jury yesterday convicted him of sexual assault and he was remanded in custody until sentencing.
Judge William Hart said: 'He bit off slightly more than he could chew with this young lady. Not everyone could do what she did and not everyone could even sensibly try to do what she did.
'I have no doubt that if she had not done what she did she would have suffered a considerably graver ordeal than she did.'
The judge said he would ask the High Sheriff to pay the victim a £500 reward because of her bravery, saying it was 'a tiny token of the court's appreciation'.
Willis had been jailed in 2011 for punching a man to the ground and then dragging his girlfriend away towards his van.
After yesterday's hearing the woman, who cannot be named, said: 'I'm glad I was able to bring this man to justice. He is dangerous and I would not like him to do the same to other women.'
- Daily Mail