Jose Mourinho's men have made a blistering start to the 2014-15 campaign, winning seven and drawing one of their opening eight matches in the top flight to open up a five-point lead over second-placed Manchester City.
United, by contrast, have struggled for consistency, with 12 points to their name as Louis van Gaal attempts to get the most out of his expensively assembled squad.
Despite the differences in their respective early-season form, Rafael believes United can topple Chelsea at Old Trafford on Sunday.
"Everyone is beatable," he told the club's official website. "We have to do our best, of course. They are playing well.
"We're playing at Old Trafford though and we've been getting results there so they are definitely beatable.
"I feel that we've been getting results here and have played some good football.
"Football is about results and, when you don't play well and draw, like on Monday night [2-2 at West Brom], of course everyone will speak. But hopefully we can play well against Chelsea and, if we get the result, it would be very positive for us and the whole team.
"I've been involved in a lot of these games. I love to play these games. They always have a great atmosphere. I'm sure Old Trafford will be very loud again.
"It will be hard because they are playing well. We just have to concentrate and do our best, and I hope we can get the result we want."
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