Competing for the first-ever adidas Trophy, the Magpies fell behind before the half-hour mark at Celtic Park following Arne Engels' penalty before Johnny Kenny's strike doubled the Hoops' advantage on the stroke of half-time.
Anthony Elanga was handed his United debut at the restart following the Sweden international's transfer from Nottingham Forest last week but Celtic extended their lead in the opening minutes of the second-half through Yang Hjun-jun's close-range effort before Liam Scales' header rounded off a difficult afternoon for Eddie Howe's side in Glasgow.
Backed by 10,000 away supporters at Parkhead, Sven Botman produced an important last-ditch block to prevent Callum McGregor from opening the scoring in the early stages of the friendly as the Dutch defender turned the Celtic captain's close-range strike onto the roof of the net after Yang's inviting cross was initially miscued by Kenny before kindly falling into McGregor's path.
Nick Pope was forced into action shortly after Fabian Schär inadvertently turned Yang's cross towards his own net, forcing the Magpies goalkeeper to react quickly and turn the ball around the right-hand post for a corner with a strong left hand.
William Osula went close to firing United ahead as the Denmark Under-21 international collected Joe Willock's pass before his deflected effort from the edge of the box was tipped over the bar by Celtic 'keeper Kasper Schmeichel.
Celtic took the lead in the 28th minute through Engels' penalty. After the Belgian midfielder was fouled inside the box by Willock, the Belgian midfielder took the resulting spot-kick, sending Pope the wrong way from 12 yards after calmly stroking the ball into the bottom right-hand corner.
Jacob Murphy, marking eight years since joining his boyhood club from Norwich City, went close to equalising for the visitors in swift fashion after connecting with Matt Targett's cross at the back post but the winger's header was comfortably held by Schmeichel.
With the half-time whistle approaching, Newcastle were dealt a further blow in the 45th minute as Kenny doubled Celtic's advantage. After Schmeichel's lengthy kick from his own box caught out the United defence, Pope was unable to head the ball clear of danger, which bounced over the Magpies goalkeeper and allowed Kenny to tap into an empty net.
Elanga was awarded his Magpies bow at the restart, one of nine changes at half-time, but it was Osula who went close to halving the deficit in the opening minutes of the second-half. After young duo Joe White and Alex Murphy combined neatly on the left flank, the latter's low cross into the box found Osula but the 21-year-old's first-time shot was saved by Schmeichel from close-range.
Celtic extended their advantage in the 52nd minute through Yang as the South Korea international got onto the end of Daizen Maeda's dangerous pass before slotting a first-time strike beyond Martin Dúbravka.
Dúbravka prevented Celtic substitute Reo Hatate from adding to Celtic's goalscoring tally as the Japanese midfielder dispossessed Jamaal Lascelles before his low drive from the edge of the box was scooped out for a corner by the Slovakian 'keeper.
In the 75th minute, however, Newcastle conceded a fourth goal of the afternoon through Scales as the Irish defender rose high from Kieran Tierney's lofted cross before guiding his header into the left-hand corner of the net.
Teenage forward Sean Neave, who joined the Magpies' Academy as a 13-year-old, was handed his first-team debut for his boyhood club in the closing stages and almost scored on his United bow in stoppage-time as the Winlaton-born youngster's header from Emil Krafth's cross was pushed away on the line by substitute goalkeeper Viljami Sinisalo.
Newcastle United: Nick Pope (Martin Dúbravka 46), Kieran Trippier (Emil Krafth 46), Sven Botman (Jamaal Lascelles 46), Sven Botman (Dan Burn 46), Matt Targett (Alex Murphy 46), Bruno Guimarães (c) (Sandro Tonali 46), Lewis Miley (Travis Hernes 76), Joe Willock (Joe White 46), Jacob Murphy (Anthony Elanga 46), Harvey Barnes (Anthony Gordon 46), William Osula (Sean Neave 76).
Subs not used: John Ruddy, Harrison Ashby, Anthony Munda.
