McDermott's side ended a run of five consecutive draws in the npower Championship as Shane Long grabbed a late winner.
Long opened the scoring from the penalty spot just before half-time and Kris Commons brought Derby level after they had spurned a host of chances.
Despite Long's brace, McDermott insisted Reading were indebted to Federici for keeping the Rams at bay.
He said: "I thought first half we were on top of the game but second half Derby came out really strong and our keeper had to make a couple of good saves. They scored a good goal and it could have gone either way but, fortunately for us, Shane Long has got a great header and we won the game."
He added: "Our keeper was first class. His kicking was good and his organisation was good. He's made saves that basically have won us the game. That's what you want from your keeper, making saves that make a difference and he's done that today."
Source: PA
Source: PA