Goals from Yakubu and Julio Arca - his first in Middlesbrough colours - were enough to pile the agony on Southgate's opposite number, Les Reed.
Reed himself will soon be going cold turkey if there are any more festive displays like this in the Charlton locker.
Reed set out his defensive stall with only one thing on his mind and that was to cling to a point at the Riverside Stadium.
His Charlton side frustrated Middlesbrough for almost half an hour, but once Boro had taken the lead there was no way back for a disappointing Addicks side.
Middlesbrough keeper Mark Schwarzer could have taken the afternoon off but for the last three minutes of the game when he was suddenly called into action.
For the rest of the time he stood and watched as Middlesbrough, with Arca at last imposing himself in midfield, took the game to Charlton.
Boro threatened right from the start with a header from Emanuel Pogatetz and a left-foot shot from Arca stretching the Charlton defence.
James Morrison might have done better after being set up by Mark Viduka, but his tame header landed straight at Scott Carson's feet.
It was Morrison again who shot tamely at Carson, but the youngster was then instrumental in setting up Boro's first goal in the 29th minute.
He and Viduka exchanged passes before setting up Yakubu, who stepped inside the challenge of Talal El Karkouri and Carson to prod the ball home from close-range.
Yakubu's sixth goal of the season saw his manager Southgate punch the air with delight.
Charlton, stung into action forced three corners in quick succession and from the final deliver El Karkouri nudged the ball agonisingly wide of the post.
Djimi Traore flashed a shot hopelessly wide with Schwarzer scrambling to get across.
Boro extended their lead on 52 minutes when Arca scored his first goal for Boro with a stinging volley from the edge of the area.
Carson and Bryan Hughes both tried in vain to keep the ball out but it crept over the line.
Morrison had a shot deflected wide as Boro forced the pace, but they were suddenly on the back foot when a goalbound shot from Amady Faye was chested clear by the immaculate defending of Jonathan Woodgate.
Arca might have had a second when he fired straight at Carson and then there was a frantic finale as Charlton suddenly sprung into action, a shot from Hughes was cleared off the line by Pogatetz after a moment of madness from Schwarzer when he failed to collect a cross.
Then Andrew Davies flung himself in the path of a shot from substitute Marcus Bent and Schwarzer then saved from both Marcus and Darren Bent in quick succession.
Referee Rob Styles handled the match superbly, but he had to resort issuing a yellow card to Jonathan Fortune, who delivered a crushing tackle on Boro substitute Malcolm Christie, which ended up with a corner flag being snapped in two.