Liverpool won 3-1 at home to the Dutch side after goals by Steven Gerrard, Dirk Kuyt and Robbie Keane.
“We felt that it would be difficult, but they didn’t change their plans,” the Spaniard told Sky Sports.
“They went with five at the back, but after the second goal we were really good. We played really well and in the second half we showed good counter attacking.
“They had a plan to defend and play counter attack. When we scored the first goal we thought they would go higher and try and keep the ball, but it was only towards the end when they changed and played with another, more offensive, player.”
Benitez was also delighted to see Keane score his first goal for the club.
He said: “It will mean a lot.
“He has been working so hard that he deserved to score. Now it is a question of when he will score in the Premier League, but at least he has scored for us and he will feel good.”