Per Mertesacker scored the only goal of the contest at Craven Cottage when he headed home from close range in the 43rd minute.
"We had a positive first half but in the second half we became sloppy with our passing and played with less pace to our game," BBC Sport quotes the Frenchman as saying.
"You have to give Fulham credit; they are a good side and they played very well. It became hard in the second half.
"We played with the handbrake on and tried to keep the lead without taking risks. We didn't give them enough problems. We lost pace and quality."
Arsenal are now third in the league table with 63 points from 34 matches.