The Royals are now in fifth spot - just three points behind second-placed Cardiff - and McDermott said: "It was a great result and we're absolutely delighted. "Scunthorpe played some good football in the first half but we bossed the game after the break and probably deserved to win.
"It's been a decent week but to get three points at Nottingham Forest on Saturday and Scunthorpe is a good few days for us. They were big wins."
The Royals boss, who reserved special praise for his goalscorers, added: "From the moment I took the job I've been positive and tried to enjoy every minute of it and try and win games rather than draw them.
"That's not going to change. We bought Ian (Harte) for £70,000 and what a fantastic bargain.
"He's got 10 goals now and is a real top guy.
"Shane (Long) was quiet in the first half and in the second half we asked our strikers to give us a lift.
"Shane did that and he scored the first goal and won the penalty for the second goal.
"He's just a terrific player."
Scunthorpe now face a massive clash against relegation rivals Crystal Palace at Selhurst Park on Saturday.
Irons boss Alan Knill said: "Up to the first goal it was even and I thought we played pretty well in the first half.
"We played OK but didn't really push on and it looked like we were waiting for something to happen.
"The first goal killed us and the penalty straight after meant it was game over."
Yet Knill is refusing to throw in the towel just yet.
He added: "We just need to stop making mistakes at the back."
