Two wins from their opening two matches have seen the Blues rise to the top of the table at the start of the campaign.
Despite setting the early-season pace, Ivanovic believes that his teammates need to be fully focused against the current champions.
"It's very important to stay focused at the beginning of the game; of course they will be motivated but so will we," Ivanovic told the club's official website. "You have to be confident about these type of games but not over-confident, because the big games are always a very close to call."
Chelsea earned a 1-0 win against United when they visited Old Trafford last season.