Bayern Munich's Matthias Sammer has justified the Bavarian giants' recent conduct towards struggling rivals Borussia Dortmund by insisting all is fair in the battle to be Germany's top team.

Bayern fought back to claim a 2-1 league win over Dortmund in Munich on Saturday to consign Borussia to their fifth straight defeat which left last season's runners-up second from bottom.

Dortmund beat Bayern to the 2011 and 2012 Bundesliga titles before Borussia romped to a 5-2 victory over the Bavarians in the 2012 German Cup final which led to Bayern signing Dortmund stars Mario Goetze and Robert Lewandowski.

Bayern have been accused of a transfer policy which specifically weakens Dortmund, something chairman Karl-Heinz Rummenigge rejected last week, but Sammer says Munich are just making sure they are Germany's top team.

"We are in a fierce competition, which we lost in 2012," Bayern's director of sport explained to Sky Sports. "Bayern are striving to be number one.

"At the moment, things aren't of optimal circumstance between the clubs, but that is the fault of top-level sport. Everyone wants to be number one."

After the 2012 German Cup final defeat, Bayern roared back by defeating Dortmund in the 2013 Champions League final and have won the Bundesliga, with Borussia as runners-up, in record time for the last two seasons.

After Bayern signed play-maker Goetze, then striker Lewandowski in the last two seasons, Borussia's Germany winger Marco Reus is the latest Dortmund star to be linked to a big-money move to Munich's Allianz Arena.

Dortmund CEO Hans-Joachim Watzke was annoyed when Rummenigge recently revealed Reus has a release clause in his contract which allows him to leave Borussia at the end of the season.

But Sammer says both sides have not always acted fairly towards each other.

"Individual events from both sides were not okay, no question," said Sammer.

"There is too much discussion at the moment of a strained relationship, but this discussion about any acrimony is totally unnecessary."