Following a goalless hour, Longelo opened the scoring for United's second-string in terrific style as the forward's strike from inside the penalty area found the top corner.
Two quick-fire goals in the final stages of the division two clash, courtesy of forwards Yannick Touré and Victor Fernández, added gloss to the scoreline as the young Magpies claimed a comfortable victory against the Cottagers along with recording their third clean sheet of the campaign in all competitions.
Longelo told nufc.co.uk: "Everyone is buzzing because we wanted to start the new year off with a win. We've done that so the momentum is high and we'll be looking to keep that going.
"The game plan was to take control of the game, keeping the ball and we knew chances would come eventually, whether that would be in the first half or second half. It just happened to come in the second and we took them all very well.
"It was important to get the second goal so we could feel a bit more secure. It was a great finish by Yannick Touré and then a good goal by Victor (Fernández). Keeping a clean sheet was also very important because it will give us a lot of confidence.
"We know we can defend well as a team but we haven't had much luck this season in terms of clean sheets. Today was about putting it right and we managed to that very well."
Longelo, who received a Premier League 2 player of the month nomination in September, was pleased to register his name on the scoresheet after scoring another eye-catching goal which took his tally to three this term.
The 20-year-old, who joined from West Ham United in the summer of 2018, admitted he was determined to add to his goalscoring total during the second half of the campaign as Newcastle take on Manchester United in their next league fixture at Leigh Sports Village next Friday.
Longelo added: "I knew Victor was going to cross it so my intentions were to make it to the back post. I saw it then landed on Yannick (Touré) who took a touch facing backwards so I told him to 'leave it, I'll take it'. I saw the top right-hand corner free so I aimed it towards there.
"For me, I'm pleased to get on the scoresheet because I know what I can do and know what I can bring to the table. It's a matter of just doing it on a daily basis.
"I think the win will also give us a massive confidence boost going into the Man United game. We know they're a very good team with good individuals but we know what we are capable of and we'll go into that game with a strong mentality attempting to get three points."
