The booing with which The Valley greeted the final whistle was understandable. It was not just that Charlton had been poor, deservedly beaten by Leicester City, it was that the home support knew a huge opportunity had been missed.
Alan Curbishley knew it, too. Charlton have only reached the FA Cup quarter-finals twice since they won the competition in 1947. For much of that time they have been outside the top flight, but they are now a top-eight Premiership team. A fifth round home draw against mid-table Championship opposition represented a wonderful chance to progress.
"For clubs like us the Cup is really important, but whatever we do it doesn't seem to work," said Curbishley. "I'm deeply upset. We had a good situation. Leicester reminded me of us six or seven years ago. They looked more determined which I'm not happy about. I don't want to see us outfought."
While Curbishley's disappointment was writ large, Craig Levein kept his elation under wraps, almost. Which was more than Jim McCahill managed. The beaming Leicester chairman even came into the press conference to hear his manager's thoughts such was his delight at a win which, given a home draw today, could be worth nearly £1m in gate receipts, television fees and prize-money.
While Levein appreciated the financial aspect of victory, which will aid his rebuilding, he was more interested in the psychological bonus. "Today is all about the fact we managed to beat a Premiership side away from home," he said. "The confidence we can gain from that will be really important in what we are trying to do at the club."
That, added Levein, was to create a younger, more energetic side. Which made it ironic that most of the key performers were veterans. Shortly before Nikos Dabizas headed Leicester into the lead from Joey Gudjonsson's free-kick Ian Walker had made a superb save to deny Bryan Hughes on one the few occasions Charlton, in the form of Talal El Karkouri's pass, showed Premiership quality.
Then, after the hard-working Shaun Bartlett had turned in Paul Konchesky's cross for an unwarranted equaliser, Danny Tiatto and Keith Gillespie kept Charlton on the back foot. Finally, Dion Dublin followed an afternoon's defending by guiding Gareth Williams' corner in off his forehead and Bartlett's shoulder.
"We need experienced players. They are vital," said Levein. "But when I arrived nine or 10 players were over 33. It is hard to have energy in a team of so many older players. It's about getting the balance right and the likes of Dublin, Gillespie and Tiatto are a great example."
Those younger players included Gudjonsson, outstanding in a holding role, and two Scots, Williams and Stephen Hughes. This trio dominated midfield, usually one of Charlton's strongest areas, and provided the platform for victory.
"We have managed to beat a Premiership side away from home and get into the quarter-finals of the cup, and the confidence we can gain from that will be really important for what we are trying to build at the club," Levein said.
So can Leicester follow Millwall in reaching the final? They are better than their position suggests - every player had either Premiership, European or international experience. Much depends on the draw, but Leicester will not be taking anything for granted.
They have only reached the sixth round themselves once in two decades, in 2001, when a home defeat to Wycombe Wanderers triggered a slide which led to relegation and administration. That old Cup romance can be a killer when it goes sour, just ask Curbishley.
Goals: Dabizas (35) 0-1; Bartlett (45) 1-1; Dublin (90) 1-2.
Charlton (4-5-1): Kiely; Young, El Karkouri, Fortune (Johansson, 70), Hreidarsson; Rommendahl (Thomas, h-t), B Hughes (Euell, 79), Holland, Murphy, Konchesky; Bartlett. Substitutes not used: Andersen (gk), Perry.
Leicester City (4-1-4-1): Walker; Maybury, Dublin, Dabizas, Stewart; Gudjonsson; Gillespie, S Hughes (Nalis, 82), Williams, Tiatto; De Vries (Connolly, 85). Substitutes not used: Hirschfeld (gk), Canero, Heath.
Referee: P Walton (Northamtonshire).
Booked: Charlton: Thomas. Leicester City: De Vries, Gillespie.
Man of the match: Gudjonsson.