Already this season, the 21-year-old midfielder had made his competitive Newcastle debut in the Carabao Cup, been handed a first Premier League appearance from the bench against Liverpool at Anfield and earned his full top flight bow when he started at Chelsea last weekend.
Then, just a minute into Tuesday night's Emirates FA Cup third round replay at Blackburn, he tried his luck from 22 yards and saw the ball fly into the net as he helped the Magpies on their way to a 4-2 victory at Ewood Park.
And he told nufc.co.uk: "I'm over the moon. Obviously playing games is great, and making your debut, but I think when score your first goal that is probably the moment you've dreamt of the most: scoring for Newcastle United.
"Whatever happens in my career, I can always say I've scored for my boyhood team, for Newcastle United, so I'm over the moon and it helps that we won the game as well.
"It probably makes this the best (milestone) so far, with debuts and not quite getting the results we wanted. Today everything fell into place.
"It took a deflection but I'm always going to claim it. You take any goal - and in 20 years' time, no-one's going to remember that it was a deflection! I think it did take a nick off someone but it went in and they all count the same."
Rovers keeper David Raya was undoubtedly caught out by a ricochet off defender Amari'i Bell, but Longstaff's powerful effort was already on target and the youngster deserved an element of good fortune for having the confidence to shoot from such range.
He explained: "It was Tim Krul in pre-season (a couple of years ago) who said 'you should shoot more from long range, because the ball wobbles and it's hard for the keeper to track.'
"So I took that to Blackpool and luckily I scored six or seven goals from outside the box there. When I found myself in a bit of space tonight, I was always going to hit it. Jamaal (Lascelles) said before the game, 'if you get a chance, shoot.' He's taking all the credit for it now but I'm over the moon that it went in. I'm buzzing."
Longstaff was one of five Academy graduates in the squad and Cal Roberts joined him in opening his goalscoring account for the Magpies.
It was Roberts' first start for United and came 1,473 days after his only previous first team appearance for Newcastle, as a substitute in a cup tie at Leicester in January 2015.
"I'm so happy for him," said Longstaff. "I know how hard he works - we've been on loan together (at Kilmarnock) and it's great for him. For him to be back up with us is brilliant for him and a goal will do his confidence the world of good so whatever the next step is for him, he'll be full of confidence.
"He's done really, really well so hopefully he can stick around for a bit."
Tuesday night's win set up a fourth round tie against Watford on Saturday, 26th January and Longstaff was delighted to help Rafa Benítez's side to progress in the competition.
"It's great," he said. "For us lads on the fringes of the team, it's another game against another Premier League team, so we get to test where we are again. We know the squad is a little stretched at the moment so we are going to get chances in these cup games, so for us it's about working hard and trying to win these games.
"To have a home tie is great and everyone's looking forward to it. We need to rest up and get ready for the Premier League games, as that is probably the main focus, but for us lads on the fringes this is the big one for us and obviously we're trying to win every game we go into."
Modest Longstaff may feel he's "on the fringes" of the team, but his goal against Blackburn came on the back of an impressive display at Stamford Bridge, and with Ki Sung-yueng on international duty and Jonjo Shelvey and Mohamed Diamé injury doubts, Longstaff could start in central midfield for a second successive Premier League match when Cardiff City come to St. James' Park on Saturday.
He smiled: "It's not my decision - that's obviously up to the manager. I thoroughly enjoyed last weekend and playing at Chelsea, it was unbelievable, so I just tried to work hard there.
"Hopefully I've put myself in the manager's thoughts but if Mo and Jonjo are fit, obviously you need the top players out there so whatever the manager thinks, I've just got to keep doing my job, trying to work hard and perform well, and just give him a little headache and try and force my way into the team.
"If not, I'll always keep working hard and I'm just waiting for the next opportunity."
Cardiff are one place and one point above the Magpies, who currently sit 18th, and Longstaff knows that the visit of the Bluebirds could be a key match in United's season.
He admitted: "It's massive. The league's so tight this year, one win can take you up a few places and it's a lot nicer looking at the table than if you're in the bottom three.
"We know it's a big game but there's still more games to come after that - more winnable games - so we've just got to keep working hard and listening to what the manager and staff are preaching and go from there.
"I think everyone is looking forward to it. It's been a tough week with the game (on Tuesday night) but it's the right start to the week with the win, so hopefully the positivity continues into Saturday."
