Chelsea's interim boss has studied how his side played against City at Eastlands in February when they lost 2-0 in a match in which Frank Lampard missed a penalty.
Benitez will rotate his squad to bring in fresh legs from the side which progressed to the Europa League semi-finals in midweek and insists he knows the key to reaching what would be his first FA Cup final at Wembley after winning the trophy at the Millennium Stadium with Liverpool in 2006.
Benitez, whose side lie in third place in the Barclays Premier League, seven points behind second-placed City, said: "They're a good team, in a good position in the table and did well against Manchester United the other day.
"We know it'll be difficult, but it's a semi-final in a massive competition.
"We know what we did wrong against them in the league and we'll make sure we don't make the same mistakes.
"They're a good team, a strong squad. They have a manager (Roberto Mancini) with experience and they have confidence at the moment. We know we'll have to do our best if we want to progress."