Lazio heap more misery on Inter
Inter, who face a trip to the Middle East for the World Club Cup in two weeks' time, stay in sixth place, seven points behind leaders AC Milan who face struggling Brescia on Saturday.
Lazio are second behind Milan on goal difference and despite having taken just five points in their previous five league outings before Friday, they still had too much firepower for Inter.
"Lazio played very well, but they had the run of the ball, not us. That was the difference between the two teams," insisted Benitez.
The Rome side were ahead after 26 minutes when Giuseppe Biava scored a freak goal.
Inter goalkeeper Luca Castellazzi pushed a cross into the path of Esteban Cambiasso whose clearance rebounded off Biava's chest and into the goal.
Mauro Zarate doubled the advantage in the 52nd minute before Macedonian international Goran Pandev cut the deficit 22 minutes later with his first goal since February.
Inter were unlucky not to be level when an Ivan Cordoba header was cleared off the line and a Wesley Sneijder drive came back off the crossbar.
Lazio made the most of their good fortune by grabbing the third in the 89th minute through Brazilian midfielder Hernanes who scored from a direct free kick.
"The reaction of the team was better in the second half," added Benitez, who was without Samuel Eto'o, the Cameroon striker banned for three matches for headbutting an opponent.
"The guys kept trying to score right until the end of the match. But it's always better to score the opening goal, otherwise you are in danger when you are trailing.
"It wasn't easy up front for us with our two best strikers, Eto'o and Diego Milito (injured) not here. We are really unlucky."
Lazio president Claudio Lotito believes the scoreline could have been even more comprehensive.
"It could have been 4-0. We had plenty of opportunities and their goalkeeper had a great match," he said.