The 20-year-old lined up in the middle of the park for the second round tie at the City Ground and looked composed throughout, despite Daryl Murphy’s header giving Forest an early lead which they held until second half stoppage time.
Salomón Rondón’s 92nd-minute leveller looked to have taken the game to penalties, but further strikes from Matty Cash and Gil Dias won it for the Championship side after a dramatic finish.
But Longstaff – who spent time on loan at Kilmarnock and Blackpool in recent seasons – was a bright spark on a difficult evening for Rafa Benítez’s men, and afterwards he told nufc.co.uk he had conflicting feelings after fulfilling a childhood ambition.
“That’s why you go out on loan – to try and prove yourself and to come back and be prepared for these nights. For me to be able to do that, it’s what I wanted to do as a young lad and it is what you dream of,” he said.
“I had a lot of my mates texting me saying, ‘you’re so lucky to be able to do this tonight’, and when you hear them say that, it makes it set in how special it is. I’m delighted to make my debut, but it’s not the result we wanted.
“We started very slowly, they scored and we were giving the ball away – we didn’t start well. But we came back into and to score in the 90th minute or whatever it was, we’ve got to really hold on and at least take the game to penalties.
“But again, with a little lapse in concentration, we got punished. But it was brilliant for me to be able to play in a game that I’ve always wanted to play in as a young lad, and to be able to walk out in front of the fans and see it was full behind the goal – even though it’s a Carabao Cup game, there was 2,500 of them, it’s unbelievable. For me, it’s a brilliant night, but it was a bittersweet ending.”
Rondón’s first goal in a black and white shirt looked to have taken the tie to penalties, but there was more drama to follow as Cash crashed in Forest’s second moments later.
Ayoze Pérez saw a penalty appeal waved away by referee Jeremy Simpson after goalkeeper Luke Steele bundled him over in the box, and Forest then made sure of their place in the third round when Dias lifted the third over Karl Darlow in the sixth minute of added time.
“We’d worked so hard to make up for the mistake we’d made at the start and when we got the goal, maybe we switched off again a little bit,” said Longstaff. “But when the goal goes in, we’ve got to do a better job of regrouping and getting focussed again, and making sure we don’t concede another sloppy goal like we did.
“We switched off and you can’t do that. We worked so hard to make up or the mistake we did make, and Rondón scored a brilliant goal – it’s a great finish. He scored his first goal for Newcastle and we’ve got to be able to do a better job of making it a better night for him as well when he does score that goal, and try and go on and win the game.
“Everyone’s disappointed, but there’s another game on Saturday and we’ll all get ready and go again.”
Longstaff featured for United throughout pre-season, scoring in the win over St. Patrick’s Athletic in Ireland.
But while he can appreciate the achievement of making a competitive bow for his boyhood club, he reckons it may take some time to fully recognise it, given the deflating final score.
“The result is what you play the game for, to win, and we’ve lost tonight so it puts a downer on it,” he said. “But hopefully in a week’s time, a month’s time or even 25 years from now when I look back on my career, I’ll say, ‘I made my debut for Newcastle United on this night’.
“But it matters now, and we’re disappointed. It’s a brilliant night for me to be able to play in the game, but we just couldn’t get the win to put the cherry on top.”
