Crystal Palace came from behind to beat London rivals Millwall 2-1 thanks to an inspired performance from Michael Olise.
The Lions had knocked out Everton and Leicester in recent years and were eyeing another scalp when Benik Afobe put them ahead early on to only further incite a partisan crowd at the Den.
At this point Patrick Vieira, a five-time winner of the competition, was heading for an unwanted first defeat as a manager in the FA Cup but his 20-year-old summer signing turned the south London derby around.
Olise equalised within a minute of the second half with a superb individual goal and turned creator before the hour mark to help Jean-Philippe Mateta head home what proved the winner of a fiery clash to send the Eagles through to the fourth round.
The wet weather in Bermondsey did little to dampen the spirits of the Millwall faithful, who greeted the Eagles players onto the pitch with boos and repeated the trick when the visitors chose to take the knee before kick-off.
Vieira had promised to play his best team and largely stuck to his word with Conor Gallagher back to boost a side missing three key players due to their African Cup of Nations commitments.
Gallagher was welcomed back to action with an accidental whack to the face which saw him need treatment after 11 minutes.
Millwall could have already been ahead by this point but Afobe fired over following a cut-back by strike partner Tom Bradshaw.
It would not take long for the forward duo to combine to good effect again in the 17th minute and this time it produced the opener albeit with a huge helping hand from Palace.
South London is ours. pic.twitter.com/OHQUgTzzFp
— Crystal Palace F.C. (@CPFC) January 8, 2022
Jack Butland, deputising for first-choice Vicente Guaita, had time to clear the ball but unwisely attempted to dribble between Bradshaw and Afobe inside his own penalty area.
The end result was the Palace goalkeeper being dispossessed and Afobe was on hand to tap into the empty net to raise the decibel levels even more at the Den.
Another cup upset seemed on the cards for Millwall who were all over their Premier League opponents but Jeffrey Schlupp tested George Long soon after before Gallagher had an effort from 20 yards go just wide.
Eagles boss Vieira was still extremely animated on the touchline as the second tier club held a slender advantage at the break after penalty appeals for a superb George Saville tackle on Eberechi Eze were waved away by referee Anthony Taylor.
With the words of their manager still ringing in the ears, Palace set about getting back on level terms and it was a 20-year-old who silenced the home fans.
Plenty of supporters were still making their way back to their seats when Olise received a pass from Gallagher on the right, cut inside and curled an effort in off the post to equalise in the 46th minute.
Last season’s Sky Bet Championship Young Player of the Year was full of confidence now and almost scored an identical second five minutes later but his shot hit the woodwork and this time bounced away to safety.
After another effort from Olise had curled over, the ex-Reading attacker did play a part in Palace’s second with 58 on the clock.
Will Hughes crucially won back possession and found Olise, who initially went on the outside of Jake Cooper before he checked back and crossed into the area for Mateta to head in from close range.
The Palace players celebrated in front of the home supporters and saw a number of objects thrown their way as a result while the away fans chucked a flare onto the pitch and let off another smoke bomb in the stand.
Following a raft of substitutions, Millwall looked to force extra-time but Mason Bennett saw a weak shot saved while Matt Smith’s stoppage-time header was straight at Butland to ensure the visitors held on.