Dave Watson's side swept aside their League One counterparts in comprehensive fashion at Little Benton, scoring in all three of the 35-minute halves in what was their first outing of pre-season.
Defender Lewis Cass opened the scoring for a young Magpies side, rising to nod in Matty Longstaff's inswinging free kick from the left as United - who fielded a number of trialists at their academy base - dominated the opening exchanges.
After Jack Robson had rattled the underside of the crossbar and Longstaff had seen his goalbound shot blocked just in front of the line, teenage frontman Thomas Cole calmly rolled home the second after the ball fell kindly for him in the box.
Two minutes into the second period, Kelland Watts nodded Kieran Aplin's inviting cross just wide of the target as Watson's youngsters continued to apply pressure.
Robson then beat his man on the right and fired over when well placed, but the hosts didn't have to wait long to add a third goal to their tally as Aplin's corner was met by Watts, whose header found the back of the net despite some last-ditch attempts to clear from the Cod Army backline.
The Magpies, who rotated their 19-man squad throughout the fixture, then went further ahead thanks to another set piece from the right. This time, it was Jack Young's delivery, and when the ball found its way to the back post Cass was there to gleefully lash home the fourth.
Thomas Allan almost added a fifth just before the end of the second period, forcing a save from the Fleetwood goalkeeper, and Mace Goodridge went close seconds into the final third.
And eventually they did add a fifth, when Allan's blistering pace took him clear of the defence and allowed him to coolly slot home.
The visitors pulled one back late on, as a forward turned home a dangerous free kick from just outside the six yard box, but this was a routine victory for Newcastle, who could have had a sixth in the dying minutes were it not for the referee's assistant deeming Elias Sorensen to have been offside before he tapped in.
