In the first quarter of an hour, Paolo Di Canio, fed by his fellow Italian Benito Carbone, put Wednesday ahead, another Italian, Francesco Baiano, equalised and Carbone put Wednesday ahead again from the penalty spot after Di Canio was brought down.
Matters then took a turn for the worse for Wednesday. The Dane Jakob Laursen hit Derby's equaliser through a crowd of players in the 26th minute. Seven minutes later the Costa Rican Paulo Wanchope put Derby ahead, and, shortly after the interval, more poor Wednesday defending allowed Baiano to add Derby's fourth.
Then Blondeau was shown the red card for a foul on Deon Burton, the British- born Jamaican international who scored Derby's fifth 15 minutes from time.
In the night's other Premiership match, Coventry City and Crystal Palace drew 1-1 at Highfield Road, where Dion Dublin put Coventry ahead after eight minutes and Jamie Fullarton equalised a minute later.