She then told her friends she wanted to go to bed.
Ennis escorted her to a mattress set up in the laundry area of the house.
She lay down and went to sleep and woke up later to find Ennis raping her.
He had ripped her shorts off so forcibly that the button was torn off.
But because she was so drunk she did not know who was violating her.
A court would later hear that the victim was "quite obviously unconscious or semi-conscious" and "could not resist" Ennis because "she was incapable of doing so".
"She was coming in and out of consciousness and had no motor skills ... there was no positive act by (her) by word or conduct to suggest that she had consented to anything you did," Judge Robert Ronayne said at sentencing this year.
She asked her attacker and he gave the name of another teenager at the party.
The victim was found soon after by her friends "bawling and sobbing" and extremely distressed.
She went to police and told them what had happened, giving the name of the teenager Ennis had used during the rape.
The victim underwent a forensic medical examination and DNA swabs were taken - her attacker had left evidence of the rape.
Ennis: cynical and devious
When he was first interviewed the day after the rape Ennis maintained he had simply helped the victim to bed and that nothing happened.
He also told police he had seen the other male teenager with the victim - something Judge Robert Ronayne was a "continuation" of Ennis' "cynical and devious attempt" to blame the youth for the rape.
"You were quite content to avoid your responsibilities and potentially have an innocent man blamed for rape," he said at sentencing.
Police interviewed the teen named by Ennis and he denied any involvement.
A voluntary DNA sample soon eliminated him from the inquiry.
Police then honed in on Ennis - who had been seen by a number of partygoers leading the victim away from the party after she said she wanted to go to bed.
They wanted to interview him again but Ennis went to ground and police could not locate him for more than two years.
When they finally tracked him down in December 2015 they had a court order compelling him to give a DNA sample.
Judge Ronayne said he accepted the victim's account and was satisfied the crime had been committed.
The Crown was permitted to call the earlier victim in that matter to give propensity evidence - meaning they could tell the jury about the earlier charge.
Jurors are not usually given information about the previous criminal offending of a person on trial, but in Ennis' case the Crown argued it was necessary, that it showed his propensity to act in a particular way.
The jury heard that the victim of the 2010 attack was 8 years old when Ennis allegedly raped her.
The first rape
She was a friend of his family and was playing at his house when he invited her into his bedroom and told her to get on his bed.
Afterwards the little girl ran home crying and told her mother that Ennis had "kissed" her.
"I was 8, I didn't know what (rape) was, I didn't know how to word it and the only thing that I could relate it to at the time was I had seen adults on TV kissing," said the complainant, now an adult.
"That's the only sexual thing that I could relate to, so that's what I told her.
"I'd never had the sex talk so I didn't know the words for (what happened)."
Three years later the girl told a school friend what had happened and the information was passed on to a teacher.
As a result, police were called in and the girl was interviewed.
"It was a silly thing to do, to lie to the police," Ennis said.
"Everyone was angry, I was scared, I'm not a bad guy."
At sentencing Judge Ronayne said Ennis' account of consensual sex was "fictional".
He said the victim was "incapable" of consenting given her intoxication and Ennis' attempt to lie about the offending was "patent, manifest and excruciating to listen to".
"You had intercourse forcibly with her knowing perfectly well that she was not consenting," he said.
"You lied to her as to who was raping her because you knew exactly what crime you were committing at the time.
"You were in effect the good Samaritan as the old male helping a heavily intoxicated (teenager) to find a safe place to sleep off her drink.
"I am sure you were very happy to be seen by others in this false light.
"She was not only very intoxicated but she was only 17 years old and you placed her in a somewhat isolated room in order to have sex with her.
"Most people seeing a 17-year-old in her state would think more about placing her in the recovery position and keeping a close eye on her rather than raping her.
"You planned your offending carefully in my view.
"You were almost 21 at the time ... I accept that you have committed another rape but, for fair trial reasons, you were not convicted.
When she found out there was another victim whose case had never made it to trial, she was even more motivated to do what she could to protect other women from Ennis.
"I did it for her - I honestly did not do this for myself.
"I made sure I did everything I could for the other girl, I didn't care about myself.
"I don't want to look like a victim ... something bad happened to me but I got through it; I just wanted to help other people and that's why I'm talking to you."
She said Ennis' offending had a huge impact on her and her family.
This statement has been abridged, but is in the victim's own words and exactly how she read it in the courtroom.
This statement may be confronting or upsetting - please take care. If you've ever experienced sexual assault or abuse and need to talk to someone call the confidential crisis helpline on: 0800 227 233 (08002B SAFE). If it's an emergency and you feel that you or someone else is at risk, call 111.
We met as children.
Now you hardly know me, yet you've been inside me - and that is why we are all here today.
All the memories are faded and hazy.
Details slip my mind, but the key memories will last a lifetime.
Progression in life for me has been on hold for over four years while I've waited to figure out if I was worth something.
I will always remember emerging from that laundry the next morning, the chilling silence that fell across the room as everyone remembered my screaming fit - mere hours before.
I was the elephant in the room at that point, nobody dared to ask me about it - and nobody seemed to know what to do.
I remember finding my phone and desperately wanting to contact someone - anyone really.
The person who called me back instantly was (my friend) and she gave me the best advice ever, advice that ultimately drove this investigation.
(She) told me to keep my undies on and NOT TO SHOWER.
For that i am eternally grateful to her because if she didn't tell me I would have never learnt your identity.
I remember being in that hospital the following night, being in that hospital chair with my feet in the air.
II felt so scared and shy of the circle of medical professionals surrounding me with their white masks and gloves on while they poked, prodded, swabbed and examined every inch of my almost naked body.
They stripped me down and took my underwear, and I finally got a chance to be alone with my body.
Standing in that hospital shower I felt dizzy like I was still intoxicated. From that moment on, I didn't want to own my body.
I looked down at my feet in the shower, the water falling onto the back of my head, dripping off my face.
My body didn't feel like mine because it was sore, I was tired and nauseous.
I wanted to take my skin off like a jacket and leave it with the nurses like the rest of my belongings they took off me.
I'll never forget the next morning, my mother calling me asking where I was…
She sounded like she had been crying - after all, she'd had two policeman knocking on her door in the middle of the night, and informing her of what had happened to me.
You went into the police station and gave your statement shortly after the investigation began, and you didn't tell them the truth.
It took two and a half years for the police to match the DNA found on my body that night, with yours.
I spent that time going crazy - 30 months of self torment, being too scared to leave my house, too scared to be around anyone consuming any form of alcohol.
The smell of alcohol on people's breath, even now nearly five years later - still takes me back to that very moment.
It took you two and a half years to admit that yes, indeed you actually did have sexual intercourse with me that night, and you only admitted it when you got caught out.
I think I cried almost every single day during that time, I lost contact with so many of my school friends simply because I wouldn't leave my house to spend time with them, they just didn't understand what I was going through.
Having never experienced proper love or having a proper boyfriend before that night, this will forever hinder my relationships with people, both friendships and intimate relationships because of a simple thing called trust.
My ability to trust someone especially if I am intimate with them is seriously halted because of what you did to me.
On the 6th of September 2015 on the two-year anniversary of that horrible night, I got my tattoo across my shoulders as an attempt to change what the day represents to me.
It says to "be your own kind of beautiful".
The "i" in the word beautiful is a semi-colon.
In literature a semicolon is used where the author chooses not to end a sentence, but allows it to flow along for longer.
There have been many times in the last few years where life feels like its not worth it, my self esteem goes down the toilet and the world feels like it's going to end.
My tattoo is a permanent reminder to keep going, to always be myself, to always try my best to love myself and tell myself that it's possible for me to someday - actually be beautiful.
I refuse to let what you did to define who I am and who I'm going to become in the future.
The really sad thing is, I hardly remember the person I was before this happened.
From what I can remember, I was an incredibly innocent kid and watching my evidential video I am amazed at how informal and immature my mannerisms were.
I have grown a very thick skin towards simple things that others take for granted like love and commitment simply because they're now my two biggest life challenges.
I have become a lonely person, yet I always have to keep my mind occupied to prevent it wandering off down those dark pathways into depression.
I took up my current job simply because I needed a job that wore me out physically every single day, and a job that I worked all my weekends and around the clock simply to keep me busy all the time.
Holding stable employment has been a huge challenge for me, I am extremely lucky to have had such amazingly supportive bosses over these few years who allow me the time and space to excuse myself from the workplace if things get too much or I simply need to have a really good cry to let all my stress and anxieties out of my system.
You know what Joseph? We wouldn't be standing here if you had just told the truth in the first place.
I always said to everyone that the only thing I wanted was to know who you were.
It took you all this time to admit that it was you on top of me, but even to this day, you still refuse to admit the seriousness of your actions.
Getting to court was always going to be a bonus for me, and a sentencing day like today seemed almost completely unrealistic.
I had no desire to punish you for what you did - it's not in my nature to be revengeful, I honestly just wanted to know the real name who that guy was that was on top of me, raping me.
What has motivated me to push through this trial is that it wasn't just me sitting at that microphone in the courtroom telling my story.
If it wasn't for the fact I am not the only one dealing with the after-effects of your actions, I probably wouldn't have made it this far.
I hope that finally, the other girl feels like I have succeeded for her, because I was the only one with the proof and the opportunity to make you understand the seriousness of what you have done to us.