The Spanish coach refused to offer any excuses for Liverpool's alarming display, in particular a first-half performance that could have seen them dead and buried before Dirk Kuyt's headed equaliser after Lucho Gonzalez's early penalty for Porto.
Benitez said: "We were really very bad in that first half, there are no excuses.
"We gave the ball away too easily and made too many mistakes. But the second half was much better. We needed to show real character and that is what we achieved.
"We were playing against a good side and we have no complaints about the result."
And when Pennant was dismissed in the second half for a second bookable offence, Benitez said: "I have no complaints about the decision. It was correct.
"Hopefully Jermaine will learn from this experience. Maybe it will produce something positive for the future, the tackle in that position was just not needed.
"It is difficult to understand why he did it, we had talked to him about staying on his feet and not making rash challenges. We were even talking on the bench about taking him off, but we just did not get the time to do it."
Liverpool were under pressure from the first whistle, and Benitez said: "We started very, very badly and it is hard to explain why because our build-up and preparation had been good.
"It was easier to do the right things in the second period, but the damage had been done. We gave the ball away far too easily, we conceded clear chances and gave away a penalty that was also a correct decision."