A fourth consecutive defeat leaves Fulham below Blackpool and Bolton at the foot of the Sky Bet Championship. but Magath believes he can revive their fortunes.
On the evidence of this showing he has a big job ahead of him after his young team collapsed despite Scott Parker's second-half equaliser which cancelled out Jamie Ward's opener.
Ward volleyed Johnny Russell's cross from the right past Jesse Joronen from eight yards in the 23rd minute but they levelled in the 54th minute when Parker 's precise low drive from 15 yards fizzed inside Lee Grant's right hand post.
But the rest of the game was a horror show for Fulham as Craig Bryson volleyed in Russell's cross in the 59th minute before Chris Martin was allowed to turn too easily two minutes later and beat the exposed Joronen.
Martin tapped in his second in the 87th minute after Simon Dawkins had gone clear to strike a post and Dawkins completed the rout a minute later when he ran through another gaping hole in the defence to complete a memorable day for Derby.
"That was the worst performance but the good thing about today is that it is clear we have to change something," Magath said. "The result was very bad and so now is the time to change. A few minutes after the game is not the time to talk about what we will change but for sure there will be new players in.
"I am convinced the quality of the players is very good but we are not getting a real team at the moment because of the losses we have not enough confidence to show what we are able to do. I have to react and bring some players in.
"I am not satisfied with the situation. Derby are one of the favourites for this season and you can lose against such a good team but not in this manner."
When he was asked if he is the right man to guide Fulham through the Championship, Magath replied: "Yes, for sure."
Derby head coach Steve McClaren was delighted with the way his team responded to the defeat at Charlton on Tuesday night.
"It wasn't so much the result, what disappointed me was the performance," he said of that match. "It wasn't Derby and we talked about that and the key thing in this league is how you react and the players have done it themselves.
"They were determined to rectify that performance and result against a very good team so the reaction was doubly pleasing because once we conceded the goal coming back was so important and in the last 15 minutes we were totally dominant.
"We certainly look at the results and the players do and we wanted to make sure we put a marker down and we've done that but it's no good doing it in one game, we've got to do it consistently."