The game was goalless when Gary O'Neil was shown a straight red card for a foul on Johnny Russell in the 60th minute, and Derby dominated from then on.
However, before the Championship play-off final could go to extra-time, Bobby Zamora scored a late goal to fire QPR back to the Premier League.
Redknapp told Sky Sports: "We were hanging on with 10 men. We were looking to maybe take the game to penalties.
"They are a good side and we had 10 men, but we worked hard and got a fantastic goal so I couldn't be more pleased.
"I'd be lying if I said I could see us scoring. They had 11 men and were probing, Rob Green was making saves."
Redknapp felt that the dismissal of O'Neil was harsh, although he acknowledged it was a poor tackle from the midfielder.
"I don't think he was the last man, there was a defender behind him. But it was a bad challenge and he (Russell) was going in on goal," he said.
"I thought were bang in trouble, but we showed great character."
Questioned on where the achievement stands in his list of career highlights, Redknapp said: "It was a one-off.
"Where do you stand on the touchline? We were hanging on for grim death and then to go and score a goal like that, it is just what makes this the best game in the world."
Asked what it means to lead the club back to the Premier League, Redknapp added: "Everything.
"I want to do it for the people here (at Wembley), the owners and the players. They are fantastic people."