Andrew Crofts’ 90th minute equaliser rescued a point for Charlton in the 1-1 draw at Southend United.
Cox opened the scoring after 26 minutes from 12 yards but the Blues were made to rue their missed chances as Crofts’ netted extremely late to steal a point for the Addicks.
Stephen McLaughlin almost put the home side ahead after 18 minutes, but his effort from range flew just past the left post.
The Blues had opened the game in an incredibly slow fashion compared to recent games but were beginning to create chances.
And their pressure eventually showed as Cox opened the scoring after 26 minutes. The former Leyton Orient front-man worked his way into space and managed to fire a left-footed effort towards goal and past Dillon Phillips to get his seventh goal of the season.
The Blues had chances to double the lead twice towards the end of the second half but Phillips denied Anthony Wordsworth and Cox from range with excellent saves.
As the clock reached the hour mark the hosts had yet another chance to double the lead. The ever-present McLaughlin cut onto his right-foot but the crossbar made sure that Charlton remained just a goal behind.
Southend ‘keeper Ted Smith produced an incredible save to deny Jordan Botaka’s shot towards the top-corner.
The visitors increased the pressure and on 70 minutes they came inches from levelling but the crossbar kept out Joe Aribo’s shot.
Marc-Antoince Fortune had the perfect opportunity to seal the victory for the Blues on 89 minutes but his header at the far post flew just wide, a miss which proved to be costly for the home side.
The Addicks ran straight up the other end following Fortune’s miss and Crofts fired a shot at goal which ricocheted off the bar before falling over the line.
The home side pushed for a winner deep into added time but Michael Timlin dragged his effort inches wide, however the Blues were left pleased as they extended their unbeaten run to twelve games.