Millwall booked an FA Youth Cup fourth round trip to Plymouth Argyle with a superb team display to beat Championship outfit Sheffield Wednesday on a freezing night at Hillsborough.
Having comfortably progressed to the third round with victories against Luton Town (2-0) and Dagenham & Redbridge (5-1), this was undoubtedly the toughest test yet faced by Scott Fitzgerald's youngsters.
And they did it the hard way, recovering from the shock of conceding a third-minute goal to battle back and secure a thoroughly deserved win.
Wednesday came flying out of the traps and forced a corner within the opening 30 seconds.
Although that was dealt with comfortably, by the third-minute Fitzgerald's side were a goal behind.
There appeared to be little danger when Tom Connelly picked up the ball 25 yards out, but a quick swing of the right boot and the young striker's shot had flown into the back of the net despite keeper Wayne Drummond getting a hand to the ball.
Instead of letting their heads drop, the young Lions responded in the best way possible with a really positive, attacking approach to the game.
Kiernan Hughes-Mason's clipped shot was held by Arron Pratt in the home goal, Jimmy Rogers had an effort just over the bar and then Danny Keen nearly produc ed a perfect finish to a flowing attack move, only to be denied by the quick reaction of Pratt, who raced off his line to avert the danger.
But there was nothing the keeper could do to deny the hungry Lions an equaliser after 26 minutes.
John Marquis created an opening on the right and although he had limited options, despatched a delicious delivery into the area that was hooked into his own net by the unfortunate Max Wragg from six yards.
Millwall squandered a gilt-edged chance to take the lead 12 minutes before the break. Jack Sim broke down the right flank and picked out Marquis with an inch-perfect cross, but the latter somehow headed over from barely three yards.
Wednesday started the second-half brightly and forced a couple of early corners.
It took a marvellous save by keeper Drummond to deny Tom Hall from point-blank range after 54 minutes - and how important that save proved to be.
Just 30 seconds later play had swung up the other end of the field and when Marquis picked up the ball 22 yards out, he took a couple of touches before rifling the ball past Pratt to the delight of the travelling Lions fans.
Seconds later Marquis' exquisite flick found the hard-working Connor French, and his low shot was held as Millwall pressed forward.
But Wednesday sensed that the game was slipping away from them and the introduction of Richard Stirrup and then Jamie Hadfield increased their urgency going forward.
A perfectly-time tackle by Omar Beckles denied Tom Hall as he prepared to pull the trigger, with Hall then drilling inches over the bar as the home side pressed forward.
Pat O'Connor - who along with defensive partner Beckles were outstanding - made a great block from Liam Palmer with James Collingham drilling wide from the resulting corner as Wednesday enjoyed their best spell of the game.
But Kiernan-Hughes Mason kept up his record of scoring in every round of the competition this season to hand The Lions a two-goal comfort zone six minutes from time.
Picking up the ball on the right, the pacey youngster weaved his way into the area, past a quartet of Owls players and then kept his cool to slot home.
It was a stunning individual effort worthy of winning any match, but this was an equally excellent team display that sees The Lions keep their FA Youth Cup dream very much alive.
Special mention should also go to the band of travelling supporters, who were in good spirits throughout despite the bitterly cold conditions, and whose vocal encouragement was clearly appreciated by coach Fitzgerald and his players.

Sheffield Wednesday: Arron Pratt, Vadaine Oliver (Richard Stirrup, 60mins), Josh Wilde (Jamie Hadfield, 67mins), James Cottingham, Nick Wood, Max Wragg, Leon Lekaj, Tom Connelly, Tom Hall, Nathan Modest, Liam Palmer (Pat Meehan, 88mins). Subs not used: Jason Mok, Andrew Sweath.
Scorer: Connelly (3mins)

Millwall: Wayne Drummond, Jack Sim, Danny Fitzsimons, Kamil Tevfik, Pat O'Connor, Omar Beckles, Kiernan Hughes-Mason, Danny Keen, John Marquis, Jimmy Rogers, Connor French (ikenna Ofoche, 82mins). Subs not used: Chris Hegarty, Connor McLaren, Hassan Janneh, Grant Ludford.
Scorers: Wragg (og 26mins), Marquis (55mins), Hughes-Mason (84mins)

Ref: R. Atkin