Benitez claimed he was waiting to shake hands with the Manchester United boss but Ferguson walked past him without doing so.
The Chelsea interim manager said: "I was waiting at the beginning. It's up to him, I was in the way waiting."
Asked why Ferguson might have done so, Benitez added: "Ask him - if you are brave enough ask him. It was his decision. I was ready and waiting. I have some education because I know a lot of people are watching so I know what I have to do."
Benitez did not attempt to shake Ferguson's hand after the conclusion of the match, which saw his side come from 2-0 down to draw 2-2.
The Spaniard explained his action by saying: "I was with my players celebrating."
United defender Rio Ferdinand could be in hot water with the Football Association after an off-the-ball altercation with Fernando Torres.
Asked if he had seen the incident, Benitez added: "I haven't. Fernando mentioned it - but you can see the replay."
Benitez insisted that Chelsea deserved to win having come from two goals down and having been denied victory by an excellent David de Gea save from Juan Mata right at the death.
He added: "We analysed the game and we deserved to win. The first half we made two mistakes and conceded two goals but in the second half we were on top of them and had a lot of chances so it was a good game."
The Chelsea boss also insisted United had had everything in their favour.
Asked if United had suffered from tiredness after their Champions League defeat by Real Madrid last week, he said: "I thought you were joking, they play on Tuesday, we play in Romania on Thursday.
"They had everything in their favour, they are playing at home, they played on Tuesday, we are coming from Romania and had to travel again so we did a great game and I'm really pleased with my players."
Benitez admitted bringing on Eden Hazard and John Obi Mikel had changed the match in Chelsea's favour - Hazard responded almost immediately with a brilliant goal.
He said: "We knew that we had to change something and we knew Hazard is a player with quality who can make a difference and he had fresh legs as well.
"I asked Frank to give 100 per cent until then and he did. You have to manage the squad.
"We saw the character and the reaction that I was expecting so until the end of the season we will be fighting."
The winners of the replay will face Manchester City in the semi-finals but such is the fixture pile-up that there is no obvious date for that replay to take place.
Benitez said: "I cannot say when I prefer, we have so many games it depends on the dates. It is an FA decision."