Sean Neave's penalty fired the Magpies ahead before the break, with Albion defender Charlie Penman sent off after committing a last man foul on the forward inside the box, before the Winlaton-born teenager doubled the hosts' lead on the stroke of half-time, turning the ball home from Kyle Fitzgerald's cross.
Despite United's advantage, Brighton halved the deficit in the opening minutes of the restart following Nehemiah Oriola's strike before Joe Belmont's close-range header before the hour mark unexpectedly saw the spoils shared at Whitley Park.
Robbie Stockdale made one change from last week's 3-0 win against Fulham as Mason Miley, brother of Magpies midfielder Lewis, replaced Leo Shahar at right-back.
Aidan Harris, who scored an incredible goal from his own half in last week's league victory against Fulham, produced the first stop of the evening as the 19-year-old goalkeeper comfortably held Nehemiah Oriola's drive from the edge of the box.
Newcastle, targeting back-to-back league wins, were unable to attempt a shot on target shortly after as Fitzgerald, who joined the Magpies from Galway United in February 2025, stabbed a dangerous pass into the penalty area after latching onto Rory Finneran's long-range pass but the ball evaded the Newcastle attackers before being cleared from the penalty area.
Neave, who made his professional debut in Newcastle's 6-1 Champions League win against Qarabağ, almost punished the Seagulls defence after pouncing on a misplaced pass on the edge of Albion's own box but the 18-year-old striker's low shot at goal was blocked by Shane Nti.
Fitzgerald went close to netting an impressive solo effort as the Irish winger collected the ball on the halfway line and after a darting run towards goal, directed a low effort inches past the left-hand post.
Newcastle were appealing for Brighton to be reduced to ten men after Aidan West, booked for a late foul on Ciaran Thompson in the opening stages, committed a strong foul on Scott Bailey but referee Aaron Jackson opted against a second bookable offence for the Albion forward.
United took the lead in the 43rd minute courtesy of Neave's penalty. After racing onto Logan Watts' lofted pass in behind the Albion backline, Neave was bundled over by Penman, who received a straight red card, before Neave scored his second spot-kick in as many games at under-21 level, drilling the ball down the middle of the net.
In the second of four additional minutes, Neave netted his 12th goal of the season at second-string level. After clever work from Fitzgerald on the right flank, the Irishman cut the ball into Neave's path who was able to scramble the ball into the net from close-range.
Newcastle's hopes of back-to-back clean sheets were ended in the 47th minute as Oriola pulled a goal back for Brighton, arriving onto Sean Keogh's dangerous cross from the left wing before rifling the ball into the roof of the net.
Neave went close to netting his second halt-trick of the season at under-21 level as a dangerous break resulted in the 18-year-old's goalbound effort inside the box being blocked out for a corner by Harry Mills.
In the 59th minute, United found themselves on level terms as Belmont drew Albion level. As Keogh's dangerous cross from the left flank was headed across the face of goal by Nti at the back post, Belmont was on hand to steer a header into the box inside the six-yard area.
Newcastle were fortunate not to fall behind as Joshua Robertson's fierce drive from the edge of the penalty area whistled wide of the right-hand post.
Anthony Munda went close to restoring the hosts' lead as the Cowgate-born midfielder, who ma latched onto Neave's neat pass before his resulting effort was pushed away by Brighton goalkeeper Steven Hall.
Seeking a late winner, Newcastle were denied a second penalty of the night in the final stages. After Mason Miley's in-swinging cross was cleared into Rory Finneran's path by Charlie Tasker, the Irish midfielder's initial shot was blocked into Neave's path before his close-range rebound looked to strike the arm of Benjamin Barclay but the decision was waved away by Jackson.
Neave ought to have grabbed his hat-trick from the resulting set-piece as Finneran's cross into the box found its way towards the teenage forward but blazed his effort wide of the target.
With stoppage-time nearing, Ciaran Thompson went close to netting a late winner as the Magpies skipper rose from Fitzgerald's inviting corner but directed a header over the crossbar.
Newcastle United Under-21s: Aidan Harris, Mason Miley, Logan Watts (Isaac Moran 90), Miodrag Pivaš, Ciaran Thompson (c), Rory Finneran, Kyle Fitzgerald, Scott Bailey (Michael Mills 46), Sean Neave, Anthony Munda, Seung-soo Park (Darren Palmer 74).
Subs not used: Adam Harrison, Baran Yildiz.
