The young Magpies conceded twice in the space of four first-half minutes in their Group C clash at Whitley Park, their second of four group fixtures in the competition following Tuesday's goalless draw against Real Sociedad, as Ayari's thunderous strike fired PSG ahead before El Idrissi's composed finish doubled the visitors' advantage.
Newcastle's youngsters were reduced to ten men before half-time as midfielder Scott Bailey received a straight red card for a foul but despite a commendable second-half display, United's second-string were unable to stage a heroic fightback against the French outfit.
With former Newcastle and PSG midfielder Yohan Cabaye in attendance, the hosts were unfortunate not to take an early lead as Seung-soo Park's corner found Ciaran Thompson at the back post but the Blyth-born defender's close-range header was steered wide of the right-hand post.
Ben Parkinson, who made his Premier League debut for the Magpies away at AFC Bournemouth during the 2023/24 season, went close to opening the scoring for United's second-string as the Durham-born forward's cross-cum shot forced PSG goalkeeper Arthur Vignaud into clawing the ball over his own crossbar.
Despite a bright start, Newcastle fell behind in the 27th following Ayari's clinical finish as the Tunisian winger slammed a ferocious angled effort beyond Magpies goalkeeper Max Thompson via the underside of the bar.
United's youngsters suffered a further blow in the 31st minute as El Idrissi extended Les Parisiens' lead, latching onto Vainqueur Diyinu Nzinga's defence-splitting pass in behind the Newcastle backline before slotting the ball underneath Thompson.
Thompson, who spent the duration of the 2024/25 campaign on loan at Chesterfield, produced an impressive stop to deny Noah Nsoki as the French teenager's dipping free-kick forced the 21-year-old 'keeper into tipping the ball over the bar.
With half-time nearing, Newcastle were reduced to ten men as Bailey received a straight red card as the Durham-born midfielder, on target in Newcastle's 2-1 UEFA Youth League win against PSG during the 2023/24 season, committed a late foul on Diyinu Nzinga before receiving his marching orders from referee Zac Kennard-Kettle to the bemusement of the hosts.
Thompson produced a strong save to prevent Rayan Abo El Nay from extending PSG's lead shortly after the restart, blocking a powerful effort at his front post before the loose ball was cleared to safety.
Despite their disadvantage, Newcastle went in search of halving the deficit as Serbian defender Miodrag Pivaš, who joined the Magpies from FK Jedinstvo Ub in the summer of 2024, rose from Alfie Harrison's free-kick but the 20-year-old's looping header was directed wide of the target.
Charlie McArthur, a representative of Scotland at under-21 level, was unable to set up a frantic finale as the Kilmarnock-born defender connected with Leo Shahar's teasing corner but saw a stooping header rise over the crossbar.
Newcastle United Under-21s are back in competitive action on Tuesday, 2nd December when facing an away trip to Scunthorpe United in their penultimate Group D fixture of this season's National League Cup [kick-off 7pm GMT].
Newcastle United Under-21s: Max Thompson, Ciaran Thompson (Leo Shahar 69), Charlie McArthur, Cathal Heffernan (c), Miodrag Pivaš (Thomas Bryant 83), Scott Bailey, Ben Parkinson, Anthony Munda, Joe Brayson (Sam Alabi 46), Alfie Harrison, Seung-soo Park (Kacey Wooster 78).
Subs not used: James Taylor, Dylan Charlton, Darren Palmer.
