1. FC Union Berlin's unbeaten start to the calendar year was broken in Leipzig as Urs Fischer's side suffered a narrow 1-0 defeat at the Zentralstadion.
Julian Nagelsmann's team, second in the Bundesliga, bagged the points at home with a 70th-minute strike from Emil Forsberg, who came off the bench a few minutes later.
RB Leipzig: Gulacsi; Klostermann, Upamecano, Halstenberg; Mukiele (Adams 77), Kampl (Forsberg 60), Sabitzer, Angelino; Olmo (Poulsen 87), Nkunku (Haidara 87), Sörloth.
1. FC Union Berlin: Luthe; Ryerson, Hübner (Gentner 76), Friedrich, Knoche, Lenz (Gießelmann 81); Griesbeck (Endo 81), Andrich; Ingvartsen, Teuchert (Dajaku 60), Awoniyi (Bülter 60)
With three games in a week, Urs Fischer utilised the squad depth at the Zentralstadion with Christopher Trimmel and Grischa Prömel dropping out to save some energy. Julian Ryerson and Sebastian Griesbeck were brought into deputise, while Cedric Teuchert replaced Sheraldo Becker who picked up a knock in the win over Leverkusen. After eight minutes, the Köpenick club played into a good position against the run of play with a superb, defence-splitting pass from Robert Andrich. The midfielder found Teuchert through on goal but the ball bobbled away from his control as he looked to build on his winning goal at the Alte Försterei last week. Union's energy and determination kept Leipzig at bay for the majority of the half, but Julian Nagelsmann's team caught a glimpse of the target in the 37th minute. Christopher Nkunku found space to the right of the Union central defenders but blazed high over the target.
Fischer's first glance to his bench was to hand a debut to Leon Dajaku and bring in Marius Bülter for fresh legs in the forward areas. Despite the home team's control of the ball, Union's first foray into the last third almost resulted in a goal but Dayot Upamecano made a fantastic intervention against Marcus Ingvartsen. Leipzig took advantage of their next opportunity and found a route past Andreas Luthe. Substitute Forsberg found an inch of space inside the box and finished off impressively with a right-foot shot in the 70th minute. Christian Gentner, Keita Endo and Niko Gießelmann were introduced as Union looked for new ideas in attack. Marcus Ingvartsen took a knock in the penalty box, but the referee Sascha Steegelman awarded no penalty. The Dane shot over shortly after and Leipzig goalkeeper Peter Gulacsi kept his handling secure in the final minutes as the Köpenick club's pressure in the final minutes came to nothing.
Next up for Union Berlin is Saturday's trip to FC Augsburg.