Newcastle's second-string fell behind inside 15 minutes of the Division Two clash following Lewis Payne's composed first-half opener at the Saints' Staplewood Training Centre.

The visitors then conceded twice in two second-half minutes following strikes from Kamari Doyle and Jimmy-Jay Morgan before Dom Ballard's penalty extended the hosts' advantage further, with Michael Ndiweni's goal in the closing stages proving a mere consolation for United's youngsters.

Three changes were made from the Newcastle side which suffered a 2-0 home defeat against Aston Villa's second-string on Monday night as 19-year-old goalkeeper Jude Smith, a representative of Scotland at under-21 level, began in-between the sticks in place of Max Thompson while Irish defender Alex Murphy replaced Charlie Wiggett in central defence.

Bremen-born forward Isaac Westendorf, who joined the Magpies in January 2022 following a successful trial, also led the line as Dylan Stephenson, who scored for Newcastle's first-team during last month's Diriyah Season Cup win over Al Hilal in Riyadh, missed out through injury.

In the 15th minute, Southampton took the lead through Saints skipper Lewis Payne as the right-back brought down a long pass over the top at pace before lifting the ball over Smith.

The first-half saw both sides forced to withdraw a player due to injury as Westendorf was replaced by fellow striker Ndiweni shortly after the half-hour mark.

In the second-half, Newcastle's task was even more difficult as Doyle doubled Southampton's goal tally, racing through towards goal before slotting the ball into the net.

In the 63rd minute, United's youngsters conceded a third as Morgan slotted the ball beyond Smith.  

Another disappointing blow followed for the young Magpies after conceding a fourth goal of the evening as Ballard, introduced from the substitutes' bench, tucked away his spot-kick after Jay Robinson was fouled inside the penalty area.

With the full-time whistle appraoching, Newcastle managed to pull a goal back through Ndiweni as the Throckley-born forward, who signed his first professional contract for his boyhood club last summer, netted his third goal across all competitions at under-21 level this term.

Newcastle United Under-21s complete their Premier League Cup campaign on Wednesday afternoon, hosting their Bristol City counterparts in Group E at Whitley Park (kick-off 1pm GMT).

Newcastle United Under-21s: Jude Smith, Harry Barclay, Niall Brookwell (c), Alex Murphy (Charlie Wiggett 47), Jordan Hackett, Nathan Carlyon, Jamie Miley (Cameron Ferguson 78), James Huntley, Josh Scott (Kyle Crossley 78), Amadou Diallo, Isaac Westendorf (Michael Ndiweni 35).

Subs not used: Max Thompson.