Sir Alex's supposed snub adds to a growing collection of incidents that mark a long-running feud between the two managers, dating back to Spaniard’s time in charge of Liverpool.
The Spaniard told reporters: "I was waiting. I have education. I knew that a lot of people were watching. Ask him if you are brave enough."
The under-pressure Blues boss was delighted by his side's performance after falling two goals down within the first 11 minutes at Old Trafford, with second-half strikes from Eden Hazard and Ramires ensuring that a replay at Stamford Bridge.
Speaking to ITV after the final whistle, Benitez believes his side were unlucky not to have taken the win that would have confirmed a semi-final date with Manchester City at Wembley, particularly after Juan Mata was denied late on by David De Gea.
He continued: "I think that, especially in the second half, we were on top of them. We created the best chances and we were controlling the game."
"He [Mata] told me that De Gea made a great save, it was so unlucky but it was a great save," he continued.
"We have to think about the first game, and afterwards we think about City. It will be tough and it will be difficult because United are a great side."