Nine-man Barnsley plunged deeper into relegation danger after being hit for six.
The terrible Tykes trailed from the fourth minute when Bradley Pritchard capitalised on goalkeeper Luke Steele’s spill to open the scoring, and then went from bad to worse.
And with his players shunning the chance to explain the catastrophe, it was left to shell-shocked boss David Flitcroft to describe the anguish in the Barnsley camp.
“It was heartbreaking at times,” he said.
“We were too fragmented, there were too many holes, we weren’t solid enough and we’ve paid the price.”
Flitcroft’s misery was compounded by straight red cards shown to Tom Kennedy and Stephen Dawson in the second half.
Both will now miss crucial games during the run-in as their team battles to avoid relegation.
But their dismissals had no impact on this result, as Barnsley had capitulated before they were ordered off.
The home side were 4-0 down when Dawson was dismissed for a two-footed lunge on Yann Kermorgant.
Kennedy followed for a professional foul just before Ricardo Fuller netted the sixth.
After Pritchard’s opener, Johnnie Jackson doubled the lead on 19 minutes before Kermorgant made it 3-0 straight after the break.
Another Steele error allowed Callum Harriott to add a fourth on the hour, with substitute Salim Kerkar prodding home number five.
The victory leaves Chris Powell’s Charlton just half a dozen points off the top six, while Barnsley drop back into the relegation zone.
Former Stoke striker Fuller, whose goal to seal the rout was his first for two months, said: “They never really had a sniff.
“I know people might say the opposition is Barnsley, but in this league, everybody can beat anybody.
“This is definitely the game of the season for us.”