Dylan Stephenson's clinical finish broke the deadlock for the young Magpies at Woodhorn Lane before Jay Turner-Cooke's terrific free-kick doubled the visitors' advantage shortly after the hour mark.

Dan Maguire swiftly halved the deficit for the hosts before United's youngsters held firm to secure a final showdown with Blyth Town at St. James' Park, bidding to lift the trophy for the first time since 2018.

In front of 1,447 spectators, a ground record for Ashington, Newcastle were fortunate not to fall behind inside the opening two minutes as Charlie McArthur was dispossessed inside his own box before the ball was played into Wilson Kneeshaw's path, who stroked a close-range effort wide of the right-hand post.

Leo Shahar, who joined the Magpies from Wolverhampton Wanderers last summer following a ten-year spell with his boyhood club, went close to netting his first goal for the club after latching onto McArthur's lofted pass but the teenage right-back, a representative of England at under-17 level, dragged a low effort wide of the target. 

In the 25th minute, Stephenson netted for Newcastle in impressive fashion, racing onto a lofted pass before thrashing the ball into the bottom right-hand corner.

Teenage goalkeeper Aidan Harris, who was named on the bench for Newcastle's UEFA Champions League Group F clash away at AC Milan in September, produced a trio of key saves before the half-time break to preserve United's advantage before half-time, holding efforts from Ben Sampson, Maguire and Kneeshaw.

In the second-half, Lucas De Bolle went close to doubling Newcastle's lead in stunning fashion as the Scotland Under-21 international's audacious lob from distance flew narrowly over the crossbar.

In the 65th minute, Turner-Cooke netted United's second of the night in excellent fashion. The 20-year-old attacking midfielder, who spent the first-half of the 2023/24 campaign on loan at Scottish Premiership side St Johnstone, curled a wonderful free-kick from the edge of the box into the top left-hand corner.

Ashington, however, reduced the deficit two minutes later through Maguire's strike, with the former Blyth Spartans and Darlington forward afforded space inside the penalty area before drilling a low effort into the net via the right-hand post.

With the full-time whistle nearing, Newcastle skipper Cathal Heffernan produced a heroic last-ditch challenge to avoid the cup tie going to a potential penalty shoot-out, with the Republic of Ireland under-19 international throwing himself towards the ball before blocking Kneeshaw's close-range effort.

Despite six minutes of stoppage-time, Newcastle's youngsters doggedly resisted Ashington's late surge and will face Northern League Division One outfit Blyth Town at St. James' Park on Tuesday, 14th May.

Newcastle United Under-21s: Aidan Harris, Leo Shahar, Ciaran Thompson, Cathal Heffernan (c), Charlie McArthur (Jordan Hackett 64), Dylan Charlton, Ellis Stanton, Jay Turner-Cooke (Alfie Harrison 90), Lucas De Bolle, Dylan Stephenson, Amadou Diallo (Kyle Crossley 61).

Subs not used: Will Brown, Joe Brayson.