Benjani and Hermann Hreidarsson's deflected strikes early in the second half did the damage as Pompey moved up to fifth.
Sanchez said: "Obviously, I can understand the fans' frustration. They have seen us play well in the first half - and they have seen us play some good stuff this season but number one for them is results and we are just not getting them.
"The perfect way is getting wins and entertaining along the way but for those fans who pay good money, entertaining comes second."
After Pompey's goals in a two-minute spell, Fulham could find no way back into a match they had dominated in the first 45 minutes.
They are left still looking for their second win of the season having beaten Bolton in August but once more Sanchez did not give his top £6million signing Diomansy Kamara a run until the last half-hour when he made a triple substitution.
Sanchez said: "I was pleased with some of our players and not so much others but I don't feel let down. The investment we've made here is for the longer term and two wins could still put us back in the middle of the table.
"They are strong and muscular and once they got ahead it was a tough task for us to get back. Both goals were deflected but to be fair a goal is a goal. It is stopping people getting the shots in which matters and we didn't do that."