Boro: Pears; McGhee (Johnson 32), McGoldrick, Elsdon, Tavernier, Maloney, Soisalo (Renton 63), Wheatley, Fewster, Pattison (Coulson 46), Mondal. Subs: Hemming (gk); O'Neill.
Going in to the game Boro were joint leaders with Fulham, but this win for the Addicks, managed by ex-Boro player Jason Euell, put them top of the table with a game in hand of Boro. Fulham, in second, are just a point behind with two games in hand and tonight take on AFC Wimbledon.
Boro started well enough and took the lead through Bradley Fewster, but by half-time Anfernee Dijksteel and Mikhail Kennedy on 30 and 43 had the home side in front.
The afternoon unravelled for Boro who found themselves 5-1 down before the hour mark as Reeco Hackett-Fairchild scored twice in a many minutes and Kennedy added his second of the afternoon.
Boro pulled one back on 75 minutes when Athletic's goalkeeper Dimitar Mitov turned into his own net, but that was nothing more than a consolation as they went down to their heaviest defeat since losing 5-1 away to Manchester City in September 2015.
They have just one game left in the group stages of the competition, at home to Wimbledon on Monday February 27th, a game scheduled for the Darlington Arena (1pm).
The next league game is against West Brom at Hartlepool United next Monday, February 20th, kick-off 7pm.