Matterson (pictured) said: "We didn't really focus too much on who we were playing because we knew we were playing a great side.
"What we did was play well. We were very enthusiastic, our kicking game was outstanding in the second half and we didn't give them a foothold back in the game. We're really happy with that.
"They created some opportunities and made some breaks but we were just desperate and the guys really believed.
"Everyone has said what a tough draw we've got - Leeds, Warrington, Bradford, Hull KR, Hull.
"But at the end of the day you have to play them all and if we concentrate on what we're doing we are going to be in all the games."
Leeds coach Brian McClennan had no complaints after his side's shock defeat.
He said: "The best team on the night won and did it well. In the last 20-25 minutes they were very good and really dominated.
"They had us in our quarter and we were struggling to get out.
"The victors get all the spoils, so well done to Castleford. They played some pretty good footy.
"Could we have gone better? Of course we could, but let's acknowledge what a good effort Castleford have made."
Leeds lost the services of Carl Ablett early on while new signing Delaney limped off in the second half.
McClennan would not comment on the nature of their injuries but said: "We were down to two subs and Castleford did well to take advantage of that.
"They really sucked the energy out of us in that last quarter and you could see us getting flatter and flatter.
"If you want to win you have got to be ruthless and they were. We've found out pretty early in 2010 that losing still stinks."