Barnsley brought 10-man Sheffield Wednesday down to earth as the Tykes recorded their third win of the season.
Iain Hume's unstoppable volley gave Barnsley the lead and the home side's task was then made easier by a straight red card for the on-loan Tony McMahon.
Jamal Campbell-Ryce then added a second-half penalty to give Barnsley further breathing space.
Substitute Leon Clarke converted the game's second spot-kick to make it 2-1 but Barnsley held on for the win.
Barnsley manager Simon Davey:
"We thoroughly deserved it. From the off we were the better side.
"They had a 10-minute spell in the second half when they got the penalty, but we could have been three or four up at half-time.
"The lads were brilliant today. They showed everything. They can play, but they showed the passion and the commitment and they worked their socks off and they deserved their win."
Sheffield Wednesday manager Brian Laws: "Defeats are hard to take in any game let alone a local derby, so I'm hurting.
"It's my first derby loss since I've been at the football club and I don't like it. I don't like the taste.
"Having said that, credit to Barnsley. Their plan to get at us early was good and I thought we looked nervy. I'd love to get my best 11 out, but I just couldn't do it."
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