The young Magpies raced into a two-goal lead inside the opening eight minutes at The Progress With Unity Stadium, with Matheos Ferreira netting his fourth goal in as many PL2 matches before Sean Neave's excellent lob doubled the visitors' lead in quick succession.
Victor Musa's header halved the deficit for the hosts after the restart but, after a resilient defensive display from Newcastle's youngsters, Anthony Munda's stoppage-time strike sealed maximum points, guaranteeing a place in the Professional Development League (PDL) play-off spot with a game to spare.
Robbie Stockdale made three changes from the side which suffered a 3-0 away defeat at Nottingham Forest three weeks ago.
Neave, who made his professional debut in the Magpies' 6-1 UEFA Champions League victory against Qarabağ FK, led the line while Ferreira and Dylan Charlton, the latter making his first U21s outing since sustaining a hamstring injury in February, were also handed starts.
Newcastle took the lead in the fourth minute through Ferreira's fine finish. After Park Seung-soo raced onto Charlton's lofted pass in-behind the Red Devils backline, the South Korean winger advanced beyond Louis Jackson before picking out Ferreira inside the box, with the Ashington-born winger stroking the ball into the net.
Newcastle extended their lead in the sixth minute as Neave netted his 14th goal of the season at under-21 level.
The Winlaton-born teenager beat William Murdock to Mason Miley's hooked clearance in behind the Man United defence before cleverly lobbing the ball over the goalkeeper on the edge of the box.
The visitors ought to have scored a third shortly after as Neave latched onto Seung-soo's pass inside the penalty area after brilliant work on the left byline by the latter, but Neave's strike was saved from point-blank range by Murdock.
Newcastle continued their pursuit for a third goal before the break as Anthony Munda, who joined United's Academy at the age of nine, headed over from Ferreira's teasing cross before, minutes later, Seung-soo's ferocious drive from the edge of the box flew narrowly over the crossbar.
Neave went close to netting his second goal of the evening on the stroke of half-time as the 18-year-old forward, a representative of England at under-19 level, completed a lengthy run from his own half before directing a drilled effort over the crossbar.
The young Magpies' clean sheet hopes were dashed as Man United pulled a goal back in the 54th minute through Musa. After a dangerous cross from the left flank worked its way to the back post, the Red Devils winger guided a firm header into the net.
Newcastle faced further attacking pressure from the hosts, managed by former Magpies Under-21s Lead Coach Adam Lawrence, as Jim Thwaites' bending free-kick from the edge of the box flew inches wide of the left-hand post.
The visitors defended valiantly in the final half-hour, with Thwaites' fierce drive from the edge of the box proving the only serious threat to Aidan Harris' goal.
With nine minutes of stoppage-time awarded, Munda confirmed three points for United in the dying stages. After racing onto Neave's pass, the ball kindly evaded Murdock as the Cowgate-born midfielder was allowed to place the ball into an empty net.
Our Under-21s conclude their 2025/26 Premier League 2 campaign on Monday 13 April when welcoming Wolverhampton Wanderers' second-string to Whitley Park [kick-off 7pm BST].
Newcastle United Under-21s: Aidan Harris, Mason Miley (Logan Watts 84), Dylan Charlton (Henry Johnson 62), Miodrag Pivaš, Ciaran Thompson (c), Rory Finneran, Matheos Ferreira (Michael Mills 73), Scott Bailey, Sean Neave, Anthony Munda, Seung-soo Park (Kyle Fitzgerald 84).
Subs not used: Adam Harrison.
