Charlton's U21s saw their four-game winning run come to an end on Friday as Barnsley ran out 2-0 victors in south Yorkshire.
Tykes forward Jack Butterfill bagged a first-half brace to condemn the young Addicks to their first defeat of the season.
Barnsley took the lead after just five minutes when Butterfill stroked home Kareem Hassan-Smith's cross.
Butterfill doubled his and Barnsley's tally midway through the opening period, converting Joe Ackroyd's corner at the near post with a fine flick.
Keegan Hartley struck the inside of the upright for the hosts on the stroke of half-time
Back came Charlton after the restart as captain Euan Williams rifled over the crossbar, before Harrison Nejman produced a last-ditch block to prevent the visitors reducing the arrears.
Daniel Kanu, who earned his full first-team debut two days earlier, forced Barnsley's stopper into a smart save after emerging from the bench as the hosts' diligent defending continued.
At the other end, Ahmed Kone produced a flying stop to keep out Fabio Jalo's late free-kick.
Williams was sent off in stoppage-time for a second bookable offence to compound the visitors' frustrations.
The young Addicks are next in action on Tuesday afternoon, when they take on Nottingham Forest in the Premier League Cup at Princes Park (2pm KO BST).
Charlton: Kone; Hobden, Mitchell, Bakrin, Dench; Adigun, Anderson, Williams (c); Ladapo, Reilly, Campbell
Subs: Trialist, Kamara, Kanu
Sent off: Williams 90+1 (second bookable offence)
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