Borussia Dortmund's teenage striker Youssoufa Moukoko became the youngest player to score in the Bundesliga but ended up on the losing side as they slumped to a 2-1 defeat at Union Berlin after conceding two set-piece goals on Friday. The 16-year-old scored on the hour mark, latching on to a Marco Reus through ball and lashing home to break the record set by Florian Wirtz, who netted for Bayer Leverkusen against Bayern Munich aged 17 years and 34 days in May 2020. Dortmund, who sacked coach Lucien Favre last week after a humiliating 5-1 defeat by promoted VfB Stuttgart and replaced him with assistant coach Edin Terzic, were lacklustre throughout as they slumped to their fifth defeat of the season. Cameroon-born striker Moukoko, who has represented Germany at youth level, had almost put his side ahead on the stroke of half-time, latching on to a Reus pass and hitting the woodwork. The hosts went ahead in the 57th minute when Taiwo Awoniyi stole in at the far post to cleverly head home Grischa Proemel's flick-on from a corner and got the winner with another header from a set piece this time by Marvin Friedrich in the 78th. The result leaves Dortmund in fourth place on 22 points from 13 games, with Union Berlin a point behind in fifth. Bayer Leverkusen are top on 28 points, with Bayern Munich and RB Leipzig a point behind them before the weekend games.