The young Magpies conceded three times in the opening 45 minutes at the Robins High Performance Centre, falling behind through Joe Low's stooping header before Sam Bell's brace extended the hosts' lead.

Newcastle's youngsters conceded a fourth six minutes after the restart as Bell completed his hat-trick, finishing from a tight angle to condemn United's second-string to a disappointing start in their Group E campaign.

Elliott Dickman made five changes from the side which suffered a 4-2 defeat against Premier League 2 Division Two leaders Leeds United as goalkeeper Will Brown replaced Jude Smith, who received an international call-up for Scotland under-21s, in-between the sticks.

There were also a first start at second-string level for Amadou Diallo since the left winger's permanent arrival on Tyneside last month after a successful trial while Charlie Wiggett, Cameron Ferguson and Jay Turner-Cooke, returning from a one-match suspension, were all handed starts against their Robins counterparts.

In the 12th minute, Newcastle were dealt a disappointing blow as Omar Taylor-Clarke's in-swinging corner found Low inside the penalty area, who powered his headed attempt beyond Newcastle goalkeeper Will Brown.

Newcastle found themselves further behind in the 16th minute through Bell's first of the afternoon, who controlled a long pass in behind the United defence before picking out Sam Pearson before the latter returned the favour to fire the ball into the net.

In the 33rd minute, Newcastle conceded a third as Pearson's close-range effort was blocked on the line before Bell made no mistake from the rebound.

A triple substitution was made at the half-time break, with striker Isaac Westendorf, Josh Scott and Lewis Miley introduced from the substitutes' bench in the hope of salvaging an almighty fightback.

However, in the 51st minute, Bristol City added a fourth as Bell completed his hat-trick, combining with Pearson before drilling a low finish past Brown from an acute angle.

Joe White, who signed a new three-year contract with the Magpies in March 2022, went close to notching a fourth goal in his last six competitive matches at under-21 level as the Carlisle-born midfielder was allowed room on the edge of the box before the 20-year-old's vicious drive towards goal was parried away by City goalkeeper Josey Casa-Grande.

Harry Barclay, who scored his first goal at under-21 level in last week's Premier League 2 defeat against Leeds, went to scoring in consecutive matches as the right-back's cross-cum shot forced Casa-Grande in pushing away the defender's inadvertent shot.

Newcastle United Under-21s will face Crystal Palace's second-string in their next Premier League Cup Group E encounter, hosting the Eagles at Whitley Park on Monday, 21st November (kick-off 7pm GMT). 

Newcastle United Under-21s: Will Brown, Harry Barclay, Niall Brookwell (c), Charlie Wiggett, Matt Bondswell, Jamie Miley (Lewis Miley 45), Joe White (Nathan Carlyon 81), Dylan Stephenson, Amadou Diallo (Josh Scott 45), Jay Turner-Cooke, Cameron Ferguson (Isaac Westendorf 45).

Subs not used: Max Thompson.