He then grabbed another woman and raped her in an alleyway, giving her 34 injuries as she screamed for help.
He paused only to kick and spit blood at passers-by who tried to stop him, reports said.
Mutambuka, originally from Rwanda, left the bar in Sunderland on December 20, 2015 and began talking to a woman on the street.
After she appeared disinterested in him, he pushed her against some shop shutters and proceeded to force his hand down her trousers.
The terrifying sexual assault came to an end when a passer-by intervened and walked the woman home.
But Mutambuka, who was 17 at the time, followed them back to her address and peered through her letterbox.
Newcastle Crown Court heard how, just a short while later, the defendant then saw another woman in the street and dragged her into an alleyway before raping her.
A member of the public attempted to stop the rape after hearing the victim’s terrified screams, but was forced to back off after Mutambuka kicked him.
The assault carried on for minutes — only to come to an end when a second man came to the victim’s rescue.
Prosecutor Andrew Espley said: ‘This was a prolonged and sustained attack.
‘There was a significant degree of planning. He wanted it to happen and took steps to make sure that it did.
“He was a man that would not be deterred. Others were present and witnessed the victim’s ordeal. The victims were alone and vulnerable.”
Mutambuka, now 18, of Gateshead, was found guilty of rape and sexual assault following a trial — with what a judge described as ‘overwhelming evidence.’
He was also found guilty of counts of assault, relating to the first man who he kicked and the second who he spat on, with spittle containing blood on 20 December 2015.
Mr. Ekwall Tiwana, defending, said that his client was very drunk at the time of the offence and had only been drunk once before in his life.
He said: “The general nature of this case is that it is a very serious offence. Although it is very serious, it is not in fact the most serious.
“This defendant was 17 at the time and had no previous convictions.
“This young man was passed from pillar to post and country to country essentially. He has been subject to a very unsatisfactory life until he moved to Newcastle and studied in Gateshead.
“He has admitted that what he did was disgraceful and disgusting. He has recognised what he did.”
The court heard how the defendant studied English, Maths and IT at Gateshead College.
The rape victim suffered 34 injuries during the attack, including reddening, abrasion and tenderness on her head, face, neck, legs and chest as well as on her genitals.
She was also punched and ‘manhandled’ during the attack.
Sentencing him to nine-year and nine-month imprisonment, Judge Robert Adams said: “This was a persistent course of conduct.
“You were sexually aroused dancing in the club and that continued when you were going home until you committed the offence.
“You were determined to have sex with a woman, regardless of her views or who she was or whatever her circumstance.
“You used violence, judging by the numerous injuries that the victim sustained.
“It is a start that you are experiencing some remorse, although it is now too late in the day.
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