Leeds United came from behind to win 2-1 against their Yorkshire rivals in McDermott's first game in charge of the club, courtesy of two Luke Varney goals.
"I told them at half time that the crowd really wanted to get behind them," McDermott told ITV Sport. I've been at places where that hasn't been the case but when we got to 1-1 it made a real difference.
"They were two very well-worked goals. The first was just over the line so I am glad the referee and linesman spotted it and the second was a fantastic bit of skill from Ross McCormack and a really good header by Luke Varney.
"Wednesday have been on a good run. You have to give them credit for that, so it was a really big win for us."
It was Leeds United's first win in eight games and moved the club up to 10th in the table.