The Magpies goalkeeper was part of a solid defensive display as Ben Dawson’s side battled their way to a 3-0 win on Tuesday night against a Leeds United side containing a number of players with first-team experience.
The performance was a far cry from the 5-0 hammering that Harker and his team-mates suffered at the hands of their Manchester United counterparts at St James's Park last Monday night.
But that defeat was put into perspective less than 24 hours later when Harker’s partner gave birth to a baby girl.
The 20-year-old stopper said: “It’s been unbelievable really.
“Obviously it was very disappointing coming out of that defeat against Manchester United, but the next morning we had a new addition to the family.
“To top the week off with a win against a good Leeds United side to reach the final of the Premier League Cup is remarkable really.
“I haven’t had many sleepless nights and my girlfriend has been helping loads by getting up during the night when I’ve had training or the game tonight.
“But the baby has been an angel and has been sleeping through really, so we can’t complain.”
United’s youngsters found themselves under heavy pressure during a first-half dominated by their hosts.
But disciplined performances from the likes of Jamie Sterry, Owen Bailey and Kelland Watts left Harker with little to do during the opening 45 minutes.
The keeper hailed the efforts of his defence and stressed his belief that they laid the foundations for an impressive win.
He said: “The lads really pulled together as a unit and that gave us the foundations to go on and win the game.
“We got a great start to the second half and we said at half-time that we just had to stay in the game for the first ten minutes.
“We knew they would come out quickly and we managed to catch them on the break. We got the penalty and after that the game took care of itself really.”
Elias Sorensen rounded off the win by grabbing the third goal of the season five minutes from time.
That meant that the Danish youngster ended a long wait to grab his 20th goal of an impressive campaign, but Harker was more impressed with a hardworking display from the striker.
“It’s great for Elias, because he’s had a tough time after the loan at Blackpool," added Harker. “Even though he could have had two goals, he’s done OK.
“To be fair to him, he’s held the ball up really well, he’s worked hard, and he’s managed to get a goal, which is great for him.”
United’s youngsters will face either Swansea City or Everton in the final after the Toffees saw off Blackburn Rovers in a quarter-final tie on Tuesday night.