The 21-year-old - currently recovering from a knee ligament injury - watched the 1-1 draw with a group of Newcastle United fans in a bar in Toronto, Canada, and described it as a "great experience."
With his season having come to a premature end after he was hurt against West Ham last month, Longstaff has enjoyed a short break in Canada as he prepares to step up his rehabilitation in the summer.
And after learning that the Toon Army Toronto supporters club were meeting to watch the match at The Peacock in College Street, Ontario, the Magpies ace came along - much to the delight of the group, which has about 150 members.
"We were going to watch the game regardless, so it was better to watch it with a few Newcastle fans," Longstaff told nufc.co.uk. "It was great - you know how big the club is but it gives you a realisation of just how big it is - you can be 3,000 miles or whatever it is from home, and there's still a Newcastle supporters club!
"It was great to meet them and talk to them; you hear their enthusiasm for the club and how much they love it, even though they're living so far away from it, so for me to watch the game with them was great.
"For me, it's still pretty weird that people can be living so far away and the second I walk in, they recognise you and they're all so happy to meet me.
"There was a few (autographs and photographs) but it was more just watching the game - it was just like going into a pub in Newcastle and watching it, really; everyone having a drink and watching the game.
"I think everyone thoroughly enjoyed it. Obviously we didn't quite do enough to hang on but when Ayo (Pérez) scored, the whole bar went up. That was great and we got to join in with them so it was a great experience.
"Like I said before, you see how far the club reaches. It's got fans everywhere and as much as you're playing for everyone in Newcastle, you're playing for fans all over the world too, which is pretty amazing when you think about it."
Longstaff visited Canada with his dad, David, who played ice hockey for Great Britain and was the first man who win 100 caps, with the pair watching Toronto Maple Leafs take on Boston Bruins.
"Hockey's something I really enjoy away from football, so it's something I've ricked off my bucket list," he said. "But hopefully next year I don't get the opportunity to go because I'm still fit and playing.
"It gave me something else to think about and it was a nice trip to end the year before the hard work starts."
Longstaff, who has made 13 appearances in all competitions, scoring twice, in his breakthrough campaign for the Magpies, added: "You want to get back on the pitch as much as possible. I got a little taste of it, playing for a couple of months, and then it got taken away so quickly, but now I want to try and get back fit as quickly as possible.
"It's going to be a tough summer - I'll probably be in most of the summer - but I'm looking forward to it. It's a new challenge, it's going to allow me to get bigger and stronger, and hopefully ready for next year.
"It'll give me a chance to get back in pre-season and hopefully try and work as hard as I can to be around the team again and see if I can get back playing some games."
