BERLIN, Dec 12 (Reuters) - Second-placed RB Leipzig slipped up with a 3-1 loss at Union Berlin on Friday for their third Bundesliga defeat of the season and missed the chance to close the gap on leaders Bayern Munich.

Leipzig stay on 29 points, eight behind Bayern who can extend their advantage with a home win over bottom side Mainz 05 on Sunday when Borussia Dortmund, third on 28, visit Freiburg.