Wenger said: "I must say Portsmouth didn't play at all in the second half. They didn't come out at all, they just defended. It was surprising to see them just making the numbers with 10 at the back.
"It was difficult because they had an experienced defence and their midfield was highly focused on defending and they had just Kanu up front.
"You cannot play like that every week. They conceded four goals last week at Liverpool and afterwards the team was just focused on defending.
"I am not disappointed with Harry Redknapp because we faced a problem and had to find a solution no matter what."
He said: "What are you supposed to do when you haven't got the ball? You can't attack if you haven't got the ball and it is very difficult to get the ball off Arsenal.
"Were we supposed to open up against them and get ripped to pieces? Is that what the game is about for us?
"And what system did they play? They played one up with (Emmanuel) Adebayor up front. I played Kanu up so that is no difference whatsoever.
"So what were we supposed to do? We stuck in there and had the best chance of the game."
That was a 75th-minute opportunity for top-scorer Benjani Mwaruwari, who had been put clear by Kanu but was tackled by Gael Clichy once he had taken the ball past goalkeeper Manuel Almunia.
Redknapp said: "He should have gone the other way. Once he pushed it that side he had a detour of about 20 yards and was never going to make it."