Chelsea travel to Old Trafford on Sunday looking to stop the champions in their tracks.
"United started very well this season but, if you remember, we started last season the same," the 27-year-old said.
"They've improved as a group but we have our aim, we have our idea and we try to use this on the pitch.
"It's going to be the hardest game for us until now and we have to show more than 100% of our power."
Ivanovic was part of the Chelsea side beaten three times by United at the end of last term, defeats which saw them crash out of the Champions League and surrender their Premier League title.
"Last season was a different situation because we had to win there, and when you play a big game away and you have to win, psychologically, it's completely different."
He added: "We have to take a good message from these two games and we have to be more motivated from those games which we lost.
"It's the first big, big test for our team, how we've improved, and we're going there trying to show our best football and to take a good result."