"It was important for Fernando and us that he has started scoring, so to get two in a derby is massive for him," Benitez said in the Liverpool Echo.
"Clearly, Fernando is a player who can change games and it is positive that he has confidence now.
"He's a threat for defenders and the only thing he is missing at the moment is his physical condition.
"When he came back from the European Championships it was important for him to rest and then train properly.
"He had an injury and he still has to improve physically. He is working so hard and he will get better - he will have more pace and be stronger.
"Fernando knows he can still improve a lot and the main thing for me is that his mentality is really good.
"He scored 33 last season but I haven't set him a target this season. If he scores 32 I will be pleased!"