Jeff Hendrick's late goal was too late as County were beaten for the sixth time in their last eight away league games.
He said: "Mark O'Brien was caught out of position for the first goal and the manner of the second goal was disappointing.
"There was a foul on Richard Keogh prior to Brighton scoring but the referee missed it. We had no decisions in the first 30 minutes of the game.
"We had two inexperienced 20-year-olds at the back and didn't have the nouse or experience that Brighton had in their side.
"But I never felt that we were out of it, even at 2-0 down. We could have been 4-0 or 5-0 down. But it wasn't and we were very spirited."
Clough was disappointed that Derby's final ball led to them not creating too many chances.
He confessed: "Our youthfulness at times will be our undoing. I didn't see too many teenagers in the Brighton side and their players know their jobs and know the game.
"We finished strongly but in the first 45 minute Brighton had two shots and scored two goals. Our final ball was not up to scratch."