The Spaniard admits cutting his losses on the misfiring striker and selling him back to Tottenham for a cut-price fee will probably cost Liverpool about £4 million for the six months he spent at Anfield.
It was a decision made in conjunction with owners Tom Hicks and George Gillett, as well as chief executive Rick Parry, and Benitez is certain it was only resolved with such speed because all of the club's powerbrokers were in the country.
How they will all feel about the risk Benitez has taken with his club's title challenge is open to question, but the manager believes Liverpool had to sell now if they were to avoid making an even bigger loss in the summer.
He said: "On Sunday, I thought he was going to stay. When we first talked with Tottenham the first idea was that we didn't want to sell him but they were pushing, and then the injury to Jermain Defoe gave them more determination.
"We were talking about players but we did not have any agreement and then on Monday we decided we had to do it with the deal we had on the table. It was good for him to play and good for us to cut our losses if things were going wrong.
"They were really interested and, initially, we did not want to sell. If we had waited until the summer and he was still not playing at the level we know he can, because of his age, waiting and delaying until then would have been worse for us.
"If they do very well, it will cost us nothing [because of performance-related bonus payments in the contract], but in a normal situation, it will cost us maybe £3-4 million."
Benitez is adamant he had no problem with Keane and, while he acknowledges both that he was responsible for the signing and was disappointed it did not end in success, believes he will be able to recapture his form in north London.
He said: "When we signed him, we thought he could be a very good partner for Fernando Torres, or that if Torres was injured he could guarantee goals. He has a lot of Premier League experience, he is a good player and he scores a lot of goals.
"But sometimes, there are lots of things that make a player not play to the level he can. Maybe there is not the understanding you need with team-mates, maybe the system is not right, maybe they are not settled in the city.
"Maybe it is that defences against Liverpool play very deep and so he did not have the space to work. You do not face that when you play for Tottenham.
"But ultimately, what do you want from a striker? Goals. What do you want from a second striker? Goals. You have to be objective. Could anyone see Robbie, playing the way he was, scoring a lot of goals for us?
"We tried to improve and fit him into the system but with us, in this club, with these team-mates and tactics he was not playing to the level he can play.
"Harry Redknapp has said he did not have a fair chance here, but that is because he is his player now and he has to support him, no matter what. But he played a lot of games here. He started a lot of games and sometimes you have to make decisions.
"We had a problem and I believe we have found the right solution. Hopefully he will go on and show what a good player he is for Tottenham."
Losing Keane leaves Benitez with a squad suspiciously lightweight up front. The Spaniard would not admit as much, but it is a mark of how threadbare his attacking options are should Torres fall victim to injury again that he namechecked both youth striker Dani Pacheco and Krisztian Nemeth, the young Hungarian international on loan at Blackpool, as potential replacements.
He said: "We have Dirk Kuyt, Ryan Babel and David N'Gog who can play as strikers, and Steven Gerrard, Yossi Benayoun and Nabil El Zhar who can play as second strikers.
"N'Gog, Pacheco, Nemeth and El Zhar are young players but they are really good, very talented. It is better you have more players with experience but in this case we had a player who wasn't playing as well as he could. Now those young players have more experience than before so our situation is a little bit better.
"It would be easier if you had five more strikers but I don't think it is a big risk for our position now. Our squad is good enough. There is a risk players get injured. That is part of the game."
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