The Royals twice came from behind to beat QPR 3-2 at Loftus Road and advance to the fourth round of the competition.
Following the victory, McDermott is now hoping that the result will kickstart the Berkshire outfit's season.
"I talked about identity and the last two games in the Barclays Premier League against Spurs and West Bromwich Albion I just feel we have not performed to a level," said McDermott.
"Our identity as a team is what you saw tonight, what we're about, and I know if we perform at that level and that tempo with the way we pass the ball with pace then we are going to be more than capable in this league. No problem.
"I felt we needed to strip the team back to what we're about, really. In the last couple of games our tempo has been slow and we haven't getting crosses into the box or creating too many chances. We really stripped the side back. We had good conversations in the dressing room and we wanted to get a result and we did that tonight."
Reading will host Arsenal in the last 16 of the tournament.