The Spain international added two first-half goals to the Champions League double he scored against Nordsjaelland in midweek to end a two-month wait to find the back of the net in the domestic competition.
Benitez said: "It's fair to say that we are watching now a Fernando with more confidence and with more belief, and at the same time, the team is the same way. I was analysing his movement before and we were adjusting little things. It's a question of confidence and just little different movements."
He added: "I have said before, if the team plays well and creates chances, Fernando will score goals.
"For me, the positive thing is that he had confidence. David has a lot of confidence, but Fernando said, 'Yes, I will take it and I will score'.
"We have three and it depends on the moment. Sometimes you have a player who has more confidence. They decide. They are players and they know how they are on the pitch."
Sunderland boss Martin O'Neill saw his side slide into the bottom three, just as they were when he took over a year ago, and Tuesday night's re-arranged home clash with Reading has assumed even greater proportions as he attempts to turn around a run of just two league wins in 23 games.
He said: "Tonight, we have dropped into the bottom three and the game that both Reading and ourselves have in hand, on Tuesday night that's over, so from that viewpoint the league will be level.
"It's a tough fight, though, it's a really tough fight. We got some fantastic results last season and it seemed by mid-February that we had calmly taken ourselves out of the relegation problems.
"I never saw it like that. I thought every game was a fight and it is exactly that now. Every game is a fight for us and we need to, when we have a foothold in games, try to make it count. That's the major point."
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