Even after shocking Eintracht Frankfurt last time out, Union were content to sit back against a side that they had never beaten at this venue. And they initially did that successfully, restricting Bayern to just a wayward long-range effort from Dayot Upamecano during the opening 20 minutes.
It seemed increasingly unlikely that the hosts would add to a measly two clean sheets from their last 15 outings as Michael Olise curled just beyond the post, before Serge Gnabry came inside to rocket over the crossbar.
Frederik Ronnow was called into his first save by Gnabry’s effort on the stroke of half-time, but Union made it to the break without being caused serious trouble.
Harry Kane was also denied from a free-kick just after the break, while it was clear that Steffen Baumgart had asked his side to be more aggressive, and their first big chance came just before the hour mark.
Josip Juranovic thundered down the right-hand side on the counter and found space to rasp one towards the near post, but stand-in stopper Jonas Urbig batted it away to avoid Union taking a surprise lead.
The situation was beginning to worry Vincent Kompany in the away dugout, but the pressure was abruptly taken off with 15 minutes to play.
Olise spotted Josip Stanisic making a brilliant underlapping run, and the Croatian duly played it across the area for Leroy Sane to nip in front of Jeong Woo-yeong and finish into the bottom left.
However, Union quickly switched to attack, and stunningly restored parity less than 10 minutes later.
Juranovic’s cross looked to be heading harmlessly to the keeper, but Urbig instead elected to parry, and Benedict Hollerbach arrived to prod in.
Although Bayern were unable to restore the lead late on, they provisionally go nine clear of the chasing Bayer Leverkusen, but that advantage could be slashed to six if Xabi Alonso’s side can take the three points from Stuttgart on Sunday.
While Union failed to record what would have been a second successive Bundesliga win for the first time since October, they can be proud of this result which edges them further from danger.
Flashscore Man of the Match: Diogo Leite (Union Berlin)
