Macauley Bonne marked his first Championship start with the goal that earned Charlton a 1-0 win at home to Leeds.
The striker, a summer signing from Leyton Orient who had previously made just two substitute appearances in the league, was in the right place at the right time to bundle home the only goal of the game.
Leeds had been knocked off top spot on Friday night by Nottingham Forest's 3-2 win at Stoke and were pushed down to fourth by this defeat, along with wins for rivals elsewhere.
Charlton joined their opponents in the play-off places, drawing level with them on 17 points.
Leeds manager Marcelo Bielsa had been in the headlines before kick-off after winning FIFA's Fair Play Award on Monday night.
That was in recognition for allowing Aston Villa to walk the ball into their net following a controversial Leeds goal towards the end of last season.
That raised a few eyebrows, not least in Derby, whose complaint to the EFL that Bielsa had sent spies to their training camp earlier in the campaign resulted in Leeds being fined £200,000.
Bielsa watched his side, whose arrival at The Valley had been delayed by traffic, put Charlton on the back foot within 30 seconds as Patrick Bamford won a corner that saw Ben White force Dillon Phillips into the game's first save.
The next quarter of an hour was scrappy but Leeds were still on top, with Mateusz Klich having a shot deflected over before a Bamford effort was blocked by Naby Sarr.
Leeds moved up a gear and Jonathan Leko did well to get in the way of Ezgjan Alioski's drive before Phillips pulled off a smart save to deny Liam Cooper, who had chested a cross goalwards.
Charlton had offered nothing of significance at the other end until they suddenly took the lead in the 32nd minute.
Their first corner of the afternoon was met by centre-back Tom Lockyer, whose thumping drive was parried by Kiko Casilla only to bounce back over the line off Bonne, who was right in front of the Leeds keeper.
Helder Costa, making his first Leeds start, fired a response over, as did Stuart Dallas a minute later.
Leeds switched to three at the back for the second half, with Kalvin Phillips dropping back from midfield.
Casilla was able to get behind Josh Cullen's free-kick while, at the other end, Lockyer almost diverted a Dallas cross into his own net.
Leeds were pushing men forward in search of an equaliser, which left them vulnerable to Charlton counter-attacks. The hosts were relieved, however, when Klich fired a decent opening well over.
Lockyer shoved Bamford after the Leeds striker had clattered Conor Gallagher, with referee John Brooks booking both transgressors with the Leeds man substituted a minute later.
White flicked a header just wide as time began to run out for Leeds, with Eddie Nketiah, one of two half-time changes by Bielsa, firing a good chance across goal and wide following a rare moment of indecision at the back from the hosts.
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Stoppage time saw Leeds pile on the pressure but keeper Phillips made a point-blank block to deny Adam Forshaw.
Charlton manager Lee Bowyer: "To beat the best team in the league is always a good achievement. I thought we deserved it. We knew we were going to be under pressure at times because everyone who plays Leeds is.
"But we held our own and tactically got it spot on. I can't praise my players any more - they are a group that never says die. To get three points just shows how far we have come as a club."
Leeds boss Marco Bielsa: "The difference between the two sides was big. We didn't impose our superiority and that was the reason for what happened. They had one shot and scored one goal.
"We had possession and controlled the game. Our players were better than their players. We didn't underestimate our opponents but we had more resources on the pitch."