Joshua Kimmich insists Bayern Munich are not thinking about Borussia Dortmund and are instead focused on ending RB Leipzig's perfect Bundesliga start.

Dortmund suffered a shock 3-1 loss to Union Berlin on Saturday to leave Leipzig as the only side with a 100 per cent record after three matches.

Bayern have won back-to-back games after being held to an opening-game draw by Hertha Berlin and face Julian Nagelsmann's league leaders in their next outing.

Kimmich has played a full part in all three of Bayern's league games so far and is relishing a top-of-the-table showdown at the Red Bull Arena on September 14.

"Dortmund's defeat hasn't been a topic yet," he told reporters. "We are now on the third matchday, we have to look after ourselves and still have work to do. 

"We've already left some points behind. There are still enough matchdays ahead of us. If we get our points, then we'll be champions again. But we still have to work hard for that.

"Leipzig got off to a perfect start with three victories. We're behind, so of course we don't want to be in that position that long. We always prefer to be right at the front. 

"We can make sure of that with the next game. In Leipzig you can set an exclamation mark. It's definitely a good time to play against Leipzig - they're in a good mood and we can see where we stand. 

"We came in with three games, now there's the international break and then it's all about Leipzig and the Champions League."

Union Berlin claimed the first Bundesliga victory in their history by seeing off Dortmund and Bayern midfielder Philippe Coutinho, handed his full debut in the 6-1 win against Mainz 05, believes that is a sign of the ruthless nature of the division.

"Dortmund are a great team," he said. "The Bundesliga is very competitive. We have to be prepared, as we are in every game. 

"We are at the beginning of the championship and we have to add as many points as we can to fight for the title at the end."