United were dumped out of the Champions League by Real Madrid on Tuesday evening, but Benitez refused to accept that his opponents could cite tiredness for allowing the Blues to force a replay after being two goals to the good within the first 11 minutes.
Asked by reporters if he felt Sir Alex Ferguson's side suffered from fatigue in the latter stages of the game, Benitez responded emphatically, claiming that Thursday's Europa League defeat to Steaua Bucuresti will have affected his own team more.
"Sorry, I thought you were joking," said Benitez. "No. They played on Tuesday [at home] and we played on Thursday in Romania, I don't think [tiredness] was an issue [for United].
"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 also claimed that Ferguson refused to shake hands with the former Liverpool boss before the game.