The EDS trailed to a sensational Scott Golbourne strike, but remained on the front foot and after Tommy Doyle restored parity, Daniel Grimshaw saved from Golbourne to win 6-5 in the shoot-out.
Harsley was pleased his side’s efforts were rewarded with a deserved victory at Montgomery Waters Meadow, where our youngsters controlled the game against League One opposition.
“I like to think most people would have thought if there was one team in normal time that was going to win it, that it would have been us," he said.
“That’s from the spirit. Some of these lads have played together for a long time and we’ve worked a lot on creating that culture.
“It’s taken time, but hopefully we’re starting to see the shoots of that coming through.
“They’re good lads. I thought we did OK in the first half, but we had more.
“We’d seen what they had and nothing was really troubling us and I told the lads we could lift it another one or two gears.
“The longer the game went on, I think we did that.”
Harsley’s team will discover their third-round opponents on Thursday evening, with the last 16 clash offering them the chance to equal last season’s run to the quarter-finals.
The youngsters are three wins from a trip to Wembley Stadium, something no Academy side has managed since being invited into the competition in 2016/17.
Harsley says his players are under no illusions on the task ahead of them and while the familiarity of being drawn against another U21 side may seem an easier proposition, the boss would prefer to face Football League opponents in the next round.
“We always have a joke, saying ‘four games from Wembley, three games from Wembley.’
“It’s just a joke, but we did it last year and it’s continued on. The lads know it’s hard.
“Hopefully we’ll come to another league club [in the next round] rather than an U21 team because this is what we’re in it for.
“We’ll play a game against an U21 team who have played Manchester City for six years and know the style of play and tactically they’ve probably started to work bits out.
“It [Football League opposition] offers something different and it’s all about getting these lads ready.”