The Belgium international scored in Napoli's 4-2 win over Lazio on Sunday as Benitez's men strengthened their grip on the final UEFA Champions League place.
It was Mertens' eighth Serie A goal since joining from the Eredivisie side and Benitez has been pleased with his progression at the Stadio San Paolo.
As well as his ability to chip in with goals, Benitez also lauded Mertens' tendency to work back and help defensively.
"I know Dries very well, I know perfectly what he can do here in Italy, he is learning to perform proficiently in his mission in the defensive phase," he said.
"He is an exemplary professional who still can improve and give us even more of the many things that he is already giving us."
Sunday's victory also saw Gonzalo Higuain score his first hat-trick for the club as Napoli bounced back from defeat to Parma last time out.
While their strong campaign has not been enough to match leading pair Juventus and Roma, they look almost certain to secure a Champions League berth this term and Benitez feels their balance can aid future progress.
"We saw three goals from Higuain, a beautiful Mertens goal and we have put on a great show for our fans, who deserve our respect," he added.
"I always say that you can play with both a good defensive phase as well as an offensive one.
"What really counts, and always has been instrumental in all the teams I've worked with, is the perfect balance between the two."
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