United's youngsters netted twice in the space of five second-half minutes, breaking the deadlock through Matt Bondswell's strike, the left-back's first goal for the club since joining in March 2021.

Niall Brookwell, who joined the Magpies' youth set-up in the summer of 2020, doubled the visitors' advantage with a close-range rebound following Joe White's missed penalty.

The victory sealed a sixth successive win in all competitions for Newcastle's second-string, who will advance into the last 16 with a game to spare should group opponents Huddersfield Town, who occupy top spot in Group G, defeat Watford in their upcoming fixture.

Elliott Dickman's side headed into the cup tie targeting six consecutive wins and faced a Birmingham side who had already suffered back-to-back 4-0 defeats against Newcastle's second-string this term.

One change was made to the starting line-up which claimed a 4-1 away win at Reading last week as Bondswell, who made his Magpies first-team debut during pre-season against Doncaster Rovers in July, replaced the injured Jay Turner-Cooke.

Newcastle were unable to register a shot on target during the opening 45 minutes, with young goalkeeper Will Brown, who joined Newcastle's Academy at the age of 13, was forced into action on a number of occasions. 

United appealed for a penalty towards the latter stages of the first-half as White, who made his Newcastle first-team debut against Rotherham United in July, went down inside the box but referee Ryan Atkin booked the 19-year-old attacking midfielder.

Targeting a breakthrough in the final 45 minutes, Newcastle forward Tom Allan - who recently returned from his loan spell at Scottish Championship outfit Greenock Morton - was introduced. 

In the 76th minute, Newcastle opened the scoring through Bondswell's header. After Allan won a free-kick deep in opposition territory, White directed the ball towards the back post before the teenage full-back headed the ball home.

United extended their lead further in the 81st minute as Brookwell registered his first goal of the 2020/21 campaign at under-23 level.

After White was awarded a penalty, the Carlisle-born youngster was unable to net consecutive spot-kicks, after scoring against Reading last week, but the loose ball fell kindly into Brookwell's path, who lashed the rebound past Birmingham goalkeeper Archie Matthews.

Newcastle United Under-23s return to Premier League 2 action on Monday, 24th February when they host Nottingham Forest at Whitley Park (kick-off 7pm GMT).

Newcastle United Under-23s: Will Brown, Nathan Carlyon, Niall Brookwell, Charlie Wiggett, Matt Bondswell, Jack Young (c), Lucas De Bolle, Adam Wilson, Josh Scott, Joe White, Cameron Ferguson (Tom Allan 67).

Subs not used: Reagan Thomson, Steven Bessent, Tom Allan, Rodrigo Vilca.