Jupp Heynckes says he could never have believed Bayern Munich would have opened up a four-point lead at the top of the Bundesliga a month ago, as his side outclassed Borussia Dortmund 3-1 in Saturday's Klassiker.

Goals from Arjen Robben, Robert Lewandowski and David Alaba were enough to seal the victory for the champions at Signal Iduna Park in an entertaining contest.

It means Bayern, who appointed Heynckes last month to replace the sacked Carlo Ancelotti, have a four-point lead over RB Leipzig, while Dortmund – who were top by five at the end of match week seven – are six adrift after 11 matches.

"We played outstanding football against a very good team, especially in the first half," he said in quotes reported by Bayern's official website. 

"One must also acknowledge that Dortmund had very good chances. But [goalkeeper] Sven Ulreich has kept us in the game. 

"The team was 100 percent motivated, we absolutely wanted to win. A big compliment to my team! 

"It was a great performance overall. Four weeks ago you could not predict that we are now six points ahead of Dortmund and four ahead of Leipzig. 

"We have worked hard for this. If we have the injured players on board again, we will play even better and hopefully successful football."

Bayern defender Mats Hummels believes Bayern were successful due to a more clinical edge in front of goal.

"It was a game with many chances on both sides. BVB could have scored more goals. But we ended up with two chances more," he said. 

"The effectiveness [in front of goal] has been the decisive factor."

On Bayern's resurgence under Heynckes, he said: "It can all turn in two, three games. That's why we have to continue to perform.

"But of course we are very happy with how the games under Jupp Heynckes have gone so far."