The teenage forward opened the scoring inside five minutes at the Academy of Light before Corry Evans' long-range drive drew an experienced Black Cats side level, fielding the likes of Bradley Dack and Pierre Ekwah.
Cathal Heffernan's header regained Newcastle's lead on the stroke of half-time before Crossley doubled United's advantage, slotting the ball home from Amadou Diallo's pass, before the young Magpies held firm for maximum points despite Joe Ryder's stoppage-time effort halving the deficit in a tense finale.
"We're all buzzing," Crossley told nufc.co.uk. "The vibes in the dressing room after winning were unreal. On the pitch, we dug in until the last minute which you can't complain about.
"It was an ideal start for the team, scoring straight away and then going in front just before half-time. It was important having that advantage, especially playing Sunderland away, and when we saw there was a lot of first-team players in their starting line-up.
"It gives you a lot more confidence. To play against footballers who are in their thirties and have had over ten years' experience at a strong level will give us a lot of belief going into the games we have coming up.
"I was sat on the touchline in stoppage-time but our whole dugout was screaming at the lads and sticking together. We defended so well in the last five minutes and gave everything we had and you saw everyone's faces when the final whistle went. We were over the moon."
Crossley, who resides in Murton, extended his goalscoring tally to six across all competitions at under-21 level this term following his brace against Sunderland.
Primarily a winger, the 19-year-old - who joined the Magpies from Morecambe in January 2020 - expressed his delight in providing a positive contribution in front of goal in an otherwise different position than usual for United's second-string.
"To get two goals was a good feeling," he added. "It's been a while and I've started to play a decent amount of minutes lately so I'm really pleased.
"As soon as I scored the first goal, and so early on, my head was down from then and I believed I was capable of scoring another. I was gutted to come off but I was all cramped up!
"I've played the number nine role at previous clubs and enjoyed it but it was good to be back there again, running in behind. I need to improve on holding the ball up but, apart from that, I really enjoyed it."
