Bayern Munich face an acid test of their status as Bundesliga leaders in Wednesday's crunch showdown when they host second-placed RB Leipzig, who know they have nothing to lose.
The Bavarian giants have won the Bundesliga title at a canter in each of the last four seasons, but Leipzig, who were only founded in 2009, have torn up the form book in their first season in Germany's top flight.
Just like Bayern, they have won 11 of their 15 league games, with three wins and a single defeat.
Both clubs have 36 points, but Munich are top on goal difference.
A shock 1-0 defeat to Ingolstadt ten days ago is the only blot on Leipzig's record having so far beaten the likes of Dortmund, Leverkusen, Schalke and now Hertha Berlin, following Saturday's 2-0 home win.
"Quick, compact and greedy -- they are the best opponent we have faced so far," was Hertha coach Pal Dardai's appraisal of Leipzig, who had gone a record 13 matches unbeaten at the start of their debut Bundesliga season.
The Bundesliga breaks for winter after this round of mid-week matches and the Allianz Arena showdown is the standout tie.
Having led for three weeks until early December, Leipzig knocked Bayern off the summit for 24 hours after their impressive win over Hertha before Munich's 1-0 victory at bottom side Darmstadt put them top again on Sunday.
Last month, Bayern's president Uli Hoeness dubbed Leipzig their "second enemy" in Germany alongside Borussia Dortmund before withdrawing the comment, but the Bavarians clearly feel threatened by Leipzig.