Eisernen made of strong stuff
Many outside observers were waiting - perhaps hoping - that this would be the game that Union's bubble would burst and, up until the hour mark it looked like it would but Urs Fischer's men showed all of the hallmarks that see them right on Bayern's tail.
In a hostile Red Bull Arena, they showed no fear but also composure not to panic and not to crack under the pressure of a side well versed in high-stakes top-of-the-table clashes.
While many squads in Union's position may wilt under the glare of the lights, they rose to the occasion in the Bundesliga's marquee match of the weekend and put Leipzig to the sword.
VAR controversy thwarts Leipzig
Marco Rose's side thought they had an 80th minute equaliser when substitute Yussuf Poulsen slid the ball past Frederik Ronnow to the point where their enthusiastic PA announcer was roaring down the mic only for referee Daniel Schlager to signal he was looking at the screen on the touchline.
It was not immediately clear what he was looking at but it was an offside call against Timo Werner in the build-up to the goal that saw it chalked off. There was some offside-related VAR controversy in the Premier League on Saturday but this was not a question of whether he was offside or not but how far back can VAR go in order to check something out.
Werner was carded for his protests and Union's led held but it left a sour taste in the mouth for those connected with Die Rotbullen.
Haberer's Puskas Award contender
When Benjamin Henrich's rasping drive from 25 yards out just to the left of goal gave Leipzig a first-half lead it was hard to fathom that there would be a better goal in this contest but he will have to take a back seat to Janik Haberer.
It was just the midfielder's fifth goal of the season and it is doubtful he has ever, or will ever, score a better one in his career.
When a corner from the Union right was glanced away at the front post, it landed on the foot of Haberer who was lurking on the edge of the box. Instead of recycling possession he swung his right boot at it and it was past Janis Blaswich in a flash.
A stunning equaliser that sent the away fans into raptures and stunned the majority of the Red Bull Arena into silence. The cleanest of volleys, the like of which you see very rarely.
Beasts from the East
For many years, since the fall of the Berlin Wall and the reunification of Germany, clubs from the old West Germany have dominated the Bundesliga. Bayern Munich are the obvious dominant force and a club from the old Eastern Bloc has never won the Bundesliga.
The likes of Dynamo Dresden, Energie Cottbus, Hansa Rostock and BFC Dynamo are all former Eastern giants who are now languishing in the lower tiers of German football so Union and RB are representing the east of the country in the upper echelons of the Bundesliga.