The young Magpies took the lead at The Brewery Field following Trevan Sanusi's penalty before the National League North outfit drew level in quick fashion courtesy of Richie Bennett's spot-kick.
Matheos Ferreira's stunning effort regained Newcastle's one-goal cushion before half-time but the visitors were pegged back for a second time following Bennett's header.
Newcastle led for a third time as 16-year-old Alfie Seldon marked his U21s debut with a goal but Robbie Stockdale's side were made to settle for a draw against the Moors following Frankie Whelan's close-range header.
Park Seung-soo, Ferreira, Mason Miley and Dylan Charlton, who all featured in the second half of the Magpies' 4-1 friendly loss at Bristol City 24 hours prior, were named in the starting 11 while 16-year-old goalkeeper George Mair was handed his first start at U21 level.
After observing a minute's silence before kick-off in honour of Kevin Keegan, who sadly passed away last week, Newcastle opening the scoring in the 19th minute through Sanusi.
The Birmingham-born winger, who made his professional debut for the Magpies in an Emirates FA Cup third round tie against Bromley in January 2025, was fouled inside the penalty area before emphatically converting his penalty, smashing the ball down the middle of the net.
United's second-string found themselves back on level terms in the 22nd minute through Bennett, sending Mair the wrong way from 12 yards.
Ferreira, who made his first-team debut for his boyhood club in last weekend's 1-1 draw against Gateshead, fired United back in front on the stroke of half-time.
The 17-year-old forward, who scored four goals in seven Premier League 2 matches last season, cut inside on the edge of the box before drilling a stunning effort into the top left-hand corner.
The interval saw Stockdale ring the changes, with Roman Dowell, Isaac Moran and Alfie Seldon making their first appearances at second-string level.
Teenage striker Afner Cá, who arrived at Newcastle last week following the expiration of the Guinea-Bissau forward's contract with La Liga side Levante, also led the line in place of Vakhtang Salia.
In the 59th minute, Newcastle's lead was distinguished as Bennett netted his and the Moors' second goal of the night, guiding his header from Jack Jenkins' pass into the far corner.
Seldon marked his first U21s appearance with a goal in the 72nd minute. The 16-year-old winger, capable of playing on either flank, got onto the end of Rory Finneran's impressive pass before sliding the ball into the bottom right-hand corner.
In the 82nd minute, Spennymoor equalised for a third time as Whelan latched onto a Trialist's looping ball before nodding the ball beyond Dowell, capping off an entertaining six-goal encounter.
Newcastle United Under-21s (first half): George Mair, Mason Miley, Dylan Charlton, Logan Watts, Miodrag Pivaš, Scott Bailey (c), Trevan Sanusi, Anthony Munda, Vakhtang Salia, Matheos Ferreira, Park Seung-soo.
Newcastle United Under-21s (second half): Roman Dowell, Henry Johnson, Luke Craggs, Isaac Moran, Rory Finneran (c), Michael Mills, Sam Alabi, Afner Cá, Baran Yildiz, Kyle Fitzgerald, Alfie Seldon.
