Charlton dropped into the relegation zone after being comfortably beaten at home by on-form Barnsley on Saturday.
Jon Macken opened the scoring for the visitors with a low shot after the clearance of Iain Hume's free-kick.
The Tykes doubled the lead with Macken following up a fine Nicky Weaver save who kept out Anderson de Silva's shot.
Darren Moore headed a third before half-time, with Charlton skipper Mark Hudson grabbing what amounts to little consolation in the 75th minute.
Charlton manager Alan Pardew:
""If that team is not good enough to beat some of the top teams then we have to accept that.
"But I'm sure that team will be good enough to get us out of the position we find ourselves in now.
"The crowd were frustrated which made it difficult for the younger players so I need to lean on the more experienced players in the squad to get us out of this situation."
Barnsley boss Simon Davey:
"We came down here with a game plan and it worked perfectly.
"To go in 3-0 up at half-time was fantastic. We were comfortable for most of the game and our first half performance was magnificent.
"We've never won at Charlton before so to come here and get a win is fantastic for the club and shows the progress we have made."
Charlton: Weaver, Moutaouakil, Cranie, Hudson, Basey, Sam (Bouazza 46), Bailey, Wright (Dickson 73), Ambrose, Varney, Gray.
Subs Not Used: Elliot, Todorov, Semedo.
Booked: Varney.
Goals: Hudson 75.
Barnsley: Muller, Foster, Guedes, Moore, Kozluk, Campbell-Ryce, Colace, De Silva, Devaney (Rigters 90), Macken (Mostto 90), Hume (Leon 72).
Subs Not Used: Hassell, Odejayi.
Booked: Foster, De Silva.
Goals: Macken 3, 17, Moore 39.
Att: 21,527
Ref: Neil Swarbrick (Lancashire).
~RS~q~RS~~RS~z~RS~52~RS~)