James Campbell, 31, admitted the attack which took place in Glasgow on August 16 last year.
Campbell, who lived with his mother in Paisley, Renfrewshire, was begging in the city when his victim stopped to check on him.
She had noticed he was not wearing a top although it was cold and raining.
The woman, 57, asked him if he was alright and chatted to him for about 10 minutes. Campbell then followed her and refused to go away.
As the woman walked past a lane, Campbell demanded a kiss before restraining and raping her.
Prosecutor Angela Gray said: "He told the woman. 'I love you. I want you to be my girlfriend,' and she replied: 'Don't be daft. I don't even know you.'"
The court heard the woman struggled with Campbell and repeatedly told him: "Please don't," and "There is no need for this."
Miss Gray added: "She repeatedly told him to stop and that he was hurting her. He did not stop and told her to shut up.
"A solicitor working in an office overlooking the lane saw the incident taking place and phoned the police."
Officers arrived to find Campbell raping the woman and dragged him off her.
The woman was visibly shaken and upset.
Campbell told police: "She wanted rough s-x so I gave it to her."
The brutal r-pe was captured on CCTV and was described by Miss Gray as 'graphic'.
She added: "It includes images of the woman and the accused in a state of partial undress."
Judge Lady Stacey placed Campbell, who has been in custody since August, last year, on the s-x offenders' register.
Lady Stacey told Campbell, who has previous convictions: "In light of the seriousness of the crime and your fairly extensive previous convictions I will see if an extended sentence is required."
Sentenced was deferred on Campbell until March 1 to obtain background reports.
Solicitor advocate Alastair Gray will give his plea in mitigation then.