
The visitors, having their best ever season, had the upper hand for an hour but could not break the deadlock until Jerome Roussillon floated a perfectly-timed left-foot cross into the path of charging Becker and the Suriname winger volleyed home.
Gladbach tried to bounce back but Marcus Thuram and Manu Kone could not beat goalkeeper Frederik Ronnow.
Union stay third on 55 points with Borussia Dortmund leading the title race on 60. Bayern Munich dropped to second place with 59 following Saturday’s 3-1 loss at Mainz 05.
Freiburg moved up to fourth spot, two points behind Union, after their 4-0 demolition of Schalke 04 earlier on Sunday.
RB Leipzig dropped to fifth on 51 after their 2-0 loss to in-form Bayer Leverkusen, who climbed to sixth on 47 and stretched their unbeaten run to eight league games.