He slept soundly before the game.
But he could hardly have dreamt of what was to follow at Ewood Park.
The Albion winger on loan to Blackburn was handed his first start as they hosted Luton Town.
A first senior goal soon followed as he held off an opponent and drilled a low shot between the keeper and the near post.
Cozier-Duberry caused excitement among Seagulls fans in the summer after his move from boyhood club Arsenal.
But, if there was some disappointment that he would go on loan, there will be delight at him now making an impact with one of the second-tier’s form teams.
Rovers boss John Eustace said Cozier-Duberry was “virtually unplayable” in the first half of a 2-0 win and also praised his defensive efforts.
Although the line-up was not confirmed until the day of the game, Cozier-Duberry knew his big day was looming.
He said: “I found out the day before in training because of the shape work we were doing.
“I found out officially in the meeting before the game and I was buzzing.
“I couldn’t wait to get out there. I slept alright but I was nervous but it was a great feeling.
“It was important to go out there and be myself, that is what the coaches told me to do.
“They wanted me to go out and show what I could do.
“They give me a lot of confidence, they have been so welcoming since I’ve come in.
“They want me to get on the ball and show what I’m about and work off the ball.
“I think there’s loads more to come, this is the start and the beginning. I won’t be complacent, I’ll keep pushing for more.”
Cozier-Duberry scored twice for Albion against Kashima Antlers as he came in off the right.
This one was different, picking up possession in the middle.
He said: “My first professional goal, it will stay in the memory.
“The ball came to me and I chopped back and luckily found the corner with my right foot,” he added.
“I got goosebumps straight away and the crowd were roaring. The fans were brilliant again and I couldn’t believe that feeling when it hit the back of the net. I went knee-sliding.
“I haven’t felt a moment like that before, not as big. Credit to everyone for this terrific run and we want to keep pushing to make sure it continues.
“The supporters have shown a lot of faith in me and it means a lot. It gives me confidence and I really appreciate that from them.”
When Cozier-Duberry scored his double in Tokyo, it felt like there was a chance he could be part of the Albion squad this season.
But chances to shine would have been limited.
His opportunities at Blackburn have been hindered by an ankle injury which proved more troublesome than initially expected.
He had made substitute appearances beforehand having come into the squad when the team were winning and found it impossible to break into the XI.
He was going to start against Swansea after the October international break but picked up the ankle injury on the Friday in training.
That ruled him out for a month and he again returned to find Rovers kept winning.
But he seized his chance against Luton and offered the pace out wide Blackburn have been missing for some time.
Cozier-Duberry, 19, follows Reda Khadra, Jan Paul van Hecke, Yasin Ayari and Andrew Moran as Albion players who have gone on loan to Ewood.
The former was probably the first player about whom Fabian Hurzeler said he judged attacking players on what they do against the ball more than on goals and assists.
That was in a packed, sweltering press room in Tokyo after the Kashima game when asked by The Argus whether Cozier-Duberry would be ready to play a part in the Premier League.
He wasn’t then and still isn’t. But he is part of a succession plan and goals, assists and performances will mean more playing time.
And that can only be good the player himself, Rovers and the Seagulls.