Mick McCarthy apologised to the Wolves supporters after seeing his side suffer a 5-1 defeat against West Brom at Molineux on Sunday afternoon.
Wolves had been hoping to move to within just a couple of points of their Black Country rivals but instead dropped back into the relegation zone following a woeful home performance.
McCarthy admitted it was an unacceptable display from his players after the final whistle and said sorry to the fans that had come to the stadium.
The manager felt Wolves had given themselves a chance at half-time after Steven Fletcher cancelled out a Peter Odemwingie opener, but poor defending after the break allowed the Baggies to run riot.
"It is an understatement to say it has been a disappointing afternoon," McCarthy told Sky Sports.
"It turned out to be a terrible afternoon, a disgraceful afternoon, in terms of our performance.
"We had weathered a (tough) first half and got back into it. We started the second half well and then failed to deal with two set-pieces, so we were 3-1 down and then we were caught on the break all over the place.
"It was an awful performance and, I don't often do it, but I'll apologise for that one to everyone who was here watching - our fans."