After seeing Fernando Torres take his goal tally to 14 with a brace, Benitez said: "It was a great performance from the team, especially in the first half.
"We looked good and created a lot of chances. But then we got a little bit nervous against a team with a very good away record.
"Torres though is always a threat. Not only that he makes room for our other players.
"He has a good mentality and experience. He uses his ability and pace to hurt defenders.
"When you have a team like ours behind you it is easy for someone like him to get chances."
Midfielder Yossi Benayoun gave David James no chance with a superb volley from 20 yards after being set up by Kewell.
Liverpool took confidence from making the breakthrough and extended their lead three minutes later.
Dirk Kuyt and Torres linked up with the Spanish striker trying to release his team-mate.
Sylvain Distin, though, got his bearings wrong and the ball came off his leg and past his own goalkeeper James.
Portsmouth pulled a goal back in the 57th minute with Benjani's ninth of the season.
He steered his effort wide of Jose Reina from the edge of the area after being set up by Kanu to stun Liverpool.
But all that did was galvanise Liverpool who regained their two-goal advantage in the 67th minute following a glorious pass from Mascherano to substitute Ryan Babel.
Babel's effort was parried by James only for Torres to find the corner from the rebound.
Torres added to his tally in the 84th minute with a clinical finish after he had been set up by Gerrard.
He said: "We started poorly then got back to 2-1 and were back in the game.
"But then we gave away two terrible goals due to poor defending.
"Torres is a top striker, a fantastic player who is at another level."
Redknapp added: "We have had a great run away from home and something to be proud of.
"Finishing in the top half of the table would be real progress for us. Anything else would be bonus."