Just two points from the summit of the Bundesliga table ahead of kick-off, BVB were hoping to make it 19 home games unbeaten, facing off against a struggling Union side who were still reeling from another last-gasp defeat in the UEFA Champions League.
Dortmund raced into an early lead for the fourth time in five fixtures when Niclas Fullkrug turned in off the post at the second attempt following a corner.
However, Union provided an instant response from a corner of their own as Robin Gosens sent a bullet header beyond Gregor Kobel.
Alex Kral then thought he’d scored his first goal in German football with a header from a set-piece, but VAR intervened for an offside. At the other end, another set-piece resulted in a disallowed goal when Marco Reus’s inswinging ball was touched in by the offside Fullkrug.
A breathless opening half-hour was then capped off with Union taking the lead from the penalty spot via Leonardo Bonucci, who became the oldest Italian goalscorer in Bundesliga history.
Die Schwarzgelben wasted no time in finding a response after the break when Nico Schlotterbeck sent a rocket into the top-right corner to restore parity. Just five minutes later, Dortmund were back ahead when Reus found Julian Brandt with a raking pass, allowing him to slam home.
An eventful contest settled down somewhat as the game passed the hour mark, with Edin Terzic’s side back in the driver’s seat.
A league-low two second-half goals in previous Bundesliga encounters this season didn’t bode well for a Union side now chasing the game, and after an impressive first-half showing, the game looked to have slipped out of reach.
Former Union player Julian Ryerson latched onto a loose ball to send a deflected effort into the net, giving BVB a two-goal lead.
Ultimately, the hosts did enough to see out the game from there, earning three points to climb to the top of the table as they continued their perfect head-to-head home record against Union.
As for Union, they remain in the bottom half of the Bundesliga standings having lost five top-flight games in a row for the first time in their history.
Flashscore Man of the Match: Marco Reus (Borussia Dortmund)