Newcastle travelled to Craven Cottage looking to record a third Premier League win in a row, but were unable to create many chances and fell to a 1-0 defeat after Ashkan Dejagah scored the only goal of the game after 68 minutes.
Striker De Jong started alongside Papiss Cisse, but the duo were starved of service in their first game without banned manager Alan Pardew, who started a three-game stadium ban.
Although the visitors dominated possession De Jong, on loan from Borussia Monchengladbach, admitted their performance was not good enough.
"We wanted to win this game, of course," he said.
"I think the game was quite boring for the fans – not much happened – and we didn't score from the moment when we had a big chance.
"Afterwards, they got a good chance and scored."
The defeat meant Newcastle dropped to ninth place in the league table behind Southampton, although they do have a game in hand on Mauricio Pochettino's side.
