MISSED the match? Catch up via beIN SPORTS CONNECT | 2-WEEK free trial

Moukoko came off the bench to net the decisive goal after Donyell Malen's opener was cancelled out by Kevin Behrens, as Dortmund edged a battle between Bayern's two closest challengers 2-1.

The victory ensures Dortmund, which was beaten 4-2 by Bayern last week, remains two points adrift of Thomas Tuchel's league leader with seven games still to play this term.

Terzic now has 32 wins from his first 50 league games in charge of Dortmund – more than any other Dortmund coach has posted in their first 50 matches at the helm – and the importance of this latest victory was not lost on the 40-year-old.

"It was a close but deserved win in an extremely important game for us," he said. "We put in a really good performance in the first half, both offensively and defensively.

"It's always difficult and always tight against Union Berlin. So we are very relieved to go home with a win.

"It is often not easy against this opponent. You can see the investment we had to make to get over the halfway line and have chances to score, and what the opponent had to invest to score.

"They are extremely dangerous on the break, and yet we managed to defend passionately at the end."

Moukoko reacted to his seventh league goal of the campaign by embracing Terzic on the touchline, and the Dortmund boss was pleased to see the young striker step up at a decisive moment.

"He's a goalscorer and has a feel for where the ball is going," he said. "I'm his coach and I want to have a close exchange with all the players – especially with such young players who have received a lot of praise in recent years.

"When they are young, they only ever hear how good they are. Then they get into senior football and realise it's not that easy.

"We want to help the boys grow up. It's extremely good for us that such a young guy once again decided the game for us."