Ferenczi grabbed the winner but Muller - being tracked by Wigan and Fulham - performed heroics with a penalty save to preserve the points.
The game turned on a breathless three-minute spell at the start of the second half after Wolves keeper Wayne Hennessey turned in a fantastic first-half display to keep out eager Barnsley.
Former Oakwell legend Mick McCarthy watched in dismay as Ferenczi stabbed in the 48th minute winner after Karl Henry tried to head Martin Devaney's curling cross away from the danger area.
Then three minutes later Wolves fans were already celebrating when Lewin Nyantanga brought down substitute Stephen Elliott in the area and handed the visitors a penalty. Andy Keogh stepped up to take the spot-kick and hit a crisp shot wide of Muller but the keeper, whose devastating form has attracted Premier League attention, dived full stretch to beat away the effort.
Hennessey had been shaping up to be star of the show as he fought tooth and nail to stretch his side's impressive run of clean sheets to six. He had to work overtime as Barnsley - unbeaten at Oakwell since the opening day - carved out a string of opportunities, but Hennessey was in defiant mood.
Star performer Jamal Campbell-Ryce forced a string of saves from Hennessey came close again with an ambitious 30-yarder that dropped over the top.
Hennessey was busy again turning away a long-range stinger from Brazilian Anderson De Silva and crowned his super first-half show with a super save to turn away a blistering 25-yard free-kick from Roberto Carlos wannabe Dominik Werling.
But then came the three minutes of drama that had Oakwell bouncing and left Tykes old boy McCarthy in misery.
Barnsley assistant manager Ryan Kidd said: "Throughout the season we have been playing well we looked a good outfit tonight and we overpowered Wolves.
"We went for 90 minutes. The first 15 minutes we looked scrappy but we controlled the game after that.
"Their keeper pulled off some great saves and we thought perhaps it wasn't going to be our night. But in the end we probably deserved more goals but defended well.
"Heinz Muller didn't have an awful lot to do but he still showed what he can do."