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.
"We're proud to have a game on Wednesday against Bayern Munich which will electrify the whole of Germany and will certainly inspire across the borders," said Leipzig's Austrian coach Ralph Hasenhuettl.
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.
RB are one of the few German clubs who have deep pockets like Bayern with the financial weight of Austrian drinks giants Red Bull behind them.
Their team has an average age of just over 23 and there is little fear ahead of their historic first Bundesliga match against Bayern.
"We want to, we can, but we don't have to," said defender Stefan Ilsanker when asked about the pressure to win in Munich.
Leipzig are set to be without injured defensive midfielder Naby Keita (thigh) and defender Marcel Halstenberg (hip), but Leipzig's young guns are relishing the test of their mettle.
"The anticipation is huge. We'll put everything into it and I can hardly wait," said centre-back Willi Orban, who scored against Hertha.
Centre-backs Orban and Ilsanker will be tasked with containing Bayern's Thomas Mueller and Robert Lewandowski, while Leipzig's top scorer Timo Werner, who has nine league goals, will face Germany's Mats Hummels.
Bayern will be missing his centre-back partner Jerome Boateng, who needs a shoulder operation.
Head coach Carlo Ancelotti says he already knows his line-up and it's more than likely Arjen Robben and Franck Ribery will start on the flanks.
While Leipzig impressed against Hertha, Bayern were lacklustre in Sunday's 1-0 win at Darmstadt which was settled by a superb goal from Douglas Costa.
"We took three very important points, without which it would have been difficult on Wednesday against RB Leipzig," said Bayern goalkeeper Manuel Neuer.
"But we can't be satisfied with the performance -- that wasn't FC Bayern today and Wednesday will be a duel between equals."
An unthinkable defeat would mean Bayern go into the winter break with the German media inevitably asking all sorts of uncomfortable questions of Ancelotti's star-studded squad.
"The respect is huge and it's going to be a demanding test. We will have to put in a top performance, a standard one isn't going to be good enough against a team like that," said Hummels.
Fixtures (All times 1900 GMT)
Borussia Dortmund v Augsburg, Borussia Moenchengladbach v VfL Wolfsburg, Hamburg v Schalke, E. Frankfurt v Mainz
Bayern Munich v RB Leipzig, Hertha Berlin v Darmstadt, Cologne v Bayer Leverkusen, Ingolstadt v Freiburg, Hoffenheim v Werder Bremen