But Hourihane made an instant impact as Swansea scored more than two in a game for the first time this season.

"I thought he was excellent, he's been so impressive since he walked through the door," Swansea boss Cooper said.

"You can see he's a real focused, professional individual who is not only going to bring what he possesses, but he also wants to buy into what we're trying to do. That's always the best way to be.

"His composure and quality on the ball was how we wanted it and why we wanted to bring him here.

"If that's the start of things to come then happy days."

Swansea, second in the Championship, have built their success this season on a watertight defence.

But Cooper's side hit top gear at the other end, with Matt Grimes and Liam Cullen both scoring twice.

Young midfielder Oli Cooper added a fifth six minutes from time with his first senior goal.

"It's a fantastic scoreline, through to the next round – that was the main objective – players making their debut, young players scoring, and loads and loads of pluses," Steve Cooper said.

"Culls (Cullen) deserved that. I said to him not so long ago, we've just been waiting for those chances to drop to him because he will score.

"We see him do it every day in training, he's a really good finisher.

"Although his finishes weren't easy, he made them look comfortable and that didn't surprise us."

Forest were outfought and outthought in a one-sided first half which saw Cullen and Grimes score to put Swansea in control.

Manager Chris Hughton's half-time words provoked a strong response from the visitors and Anthony Knockaert halved the deficit after 56 minutes.

But the Forest revival ended quickly after referee Kevin Friend awarded Swansea a penalty five minutes later, much to the fury of Hughton.

Ryan Manning fell just inside the area under a challenge from Joe Worrall, but Hughton felt the Swansea player had initiated the contact.

He said: "We were having our best period of the game and had got back to 2-1, but then the ref makes a dreadful decision.

"I was quite confident from where I was that it wasn't a penalty. I've seen it again, and it isn't, and of course it changes the game.

"I don't like to use the word diving, but from the angles I've seen there's no contact.

"The lad drags his leg a little bit and it's certainly simulation.

"If the referee has to make a decision there he has to give the lad who's gone down a booking. That is quite obvious."

Hughton was disappointed with Forest's overall performance, saying: "We made too many mistakes.

"Even though Swansea made a fair few changes, what they are is a team in a confident mood.

"We made too many errors, which you can't afford to do against a form team."

Swansea midfielder George Byers, meanwhile, has joined League One Portsmouth on loan for the rest of the season.