Sheffield Wednesday lost at home for the first time this season as they were beaten by promotion rivals Charlton.
Johnnie Jackson scored the only goal when he curled a free-kick from 20 yards into the top corner after Reda Johnson had fouled Bradley Pritchard.
Bradley Wright-Phillips could have made it 2-0 when he was put through but he could not beat goalkeeper Nicky Weaver.
Ben Hamer saved two headers from Johnson and blocked a shot from Chris Lines as Wednesday failed to equalise.
Charlton remain four points clear at the top of League One ahead of Sheffield United, while Wednesday drop down to fourth place in the table.
VIEWS FROM THE DRESSING ROOM
Sheffield Wednesday manager Gary Megson told BBC Radio Sheffield:
"I'm disappointed, I think everybody is disappointed not just with the result, but with the way that we played.
"It's nowhere near like how we've been playing and not just in the last few weeks but all season.
"I think you have to give credit to the opposition they're a good side, hard to break down and it was vital that you scored the first goal against them and we didn't do that."
Charlton Athletic manager Chris Powell told BBC London 94.9:
"I think every single Charlton supporter will be proud of the team this evening. They saw a team that really wants to do something together.
"They worked extremely hard. The will to win was there and it was a fantastic piece of quality to win it.
"We stood up to it all today. We like going away and Sheffield like to play at home - something had to give and it went our way."