This was a victory to be cherished as much by those overseeing Fulham’s academy as the management of a revived first-team. For the first time since the turn of the century, and admittedly after a lengthy spell in the top flight themselves, this club have beaten opponents from a higher division. That they did so with a youthful, virtually homegrown team merely added to the sense of achievement. Their kids are better than all right. The conveyor belt is gloriously productive.

It took a goal from Lasse Vigen Christensen, who had actually joined the youth ranks from Midtjylland at the age of 17, to see off a disjointed and disappointing Middlesbrough. The Dane sprinted into the clutter of the six‑yard box to poke in Scott Malone’s low centre, after excellent initial work from the young Luca de la Torre, seven minutes from the end of extra-time. In truth the whole contest ended up feeling like a prolonged tribute to the work of Huw Jennings and his coaching staff back at Motspur Park. Boro may have had the initial swagger and the weighty experience, but they were still eclipsed.

A first defeat since mid-March will have been a shock to the system for Aitor Karanka and his team, but they had actually been relieved even to take this game into the extra period. The slickly impressive nature of Fulham’s display had arguably seemed more significant in the wake of the frustration voiced by Slavisa Jokanovic at the weekend.

The Fulham manager’s criticisms had exposed the schism with the statistical recruitment director Craig Kline, a friend of the owner’s son, whose “Both Boxes Checked” analysis programme now dictates transfer policy in these parts. Jokanovic wanted Manchester United’s Andreas Pereira, recommended by José Mourinho, to join on loan. Kline apparently does not have enough data to assess the player’s numbers at present. As a result, the deal is off.

Jokanovic, who has “no plans to leave”, has at least seen Ragnar Sigurdsson, the scourge of England in Nice, join this week and could bask in a sense of “pride” at the performance mustered by the second-string – there were nine changes from Saturday – with this evidence of quality nurtured from within. There was the scuttling Adetayo Edun on the flank and the assured Dennis Adeniran in central midfield, both products of a buoyant academy. The latter was unperturbed by an early booking and demonstrated maturity beyond his 17 years.

The substitute Sean Kavanagh, born in Dublin but schooled at Motspur Park, had a curled attempt nodded from the goal-line by Ben Gibson while, much earlier in the evening, another youth-team graduate, Cauley Woodrow, had been denied from point‑blank range by Brad Guzan and then Daniel Ayala. Ryan Sessegnon, a scorer at 16 on Saturday, could kick his heels on the bench all night.

Woodrow’s presence had eventually panicked Julien de Sart into converting into his own net early in the second half after Ryan Tunnicliffe’s burst and Malone’s shot had squirmed away from the Boro goalkeeper, an equaliser the hosts fully merited, with Boro becalmed right up to the moment David Nugent looped a header on to the crossbar seconds from the end of normal time. The chance had virtually been the visitors’ first since the striker guided an eighth-minute header from Fábio da Silva’s delivery beyond Jesse Joronen. Thereafter, it had been Fulham’s busy, energetic style, with Tunnicliffe such a reassuring presence at their core, which had always threatened to prevail.

The winner was eventually tapped in by Christensen, a player who had signed a new contract this week, with Boro utterly unable to rouse themselves in response. Their own midfield had been far too pedestrian in the face of such energy. Guzan, whose nervy mannerisms tend to suggest panic is setting in, was as busy as he had been for most of last season at Aston Villa. Karanka ended up apologising to the travelling support, but Fulham will believe Bristol City in the third round represents a winnable tie, not least because there is life after Patrick Roberts and Moussa Dembélé. The present and future feel full of promise.