- Jordan Pefok (32')
- Sheraldo Becker (38')
- Willi Orbán (83')
Union, who move into second place with seven points behind Borussia Monchengladbach on goal difference, struck twice in six minutes with Jordan Pefok in the 32nd and Sheraldo Becker in the 38th, scoring with two of their three shots on goal in the first half.
- Don't have ESPN? Get instant access
United States international Pefok, who also assisted on the second goal, now has three goals in four games to continue his impressive start to life at his new club.
Leipzig had hit the post with Timo Werner early on but had to wait until the 83rd minute for Willi Orban to cut the deficit with a powerful header and trigger a late fight for Domenico Tedesco's team, however they failed to find an equaliser.
German Cup holders Leipzig, who lost the Super Cup to Bayern Munich last month, have drawn two and lost one of their three league games so far. They are in the group stage of the Champions League having finished fourth ahead of Union last season.
Union, unbeaten for a club record 10 consecutive league games stretching back to last season, have now put in their best ever start to a Bundesliga season.
Champions Bayern, on six points, are in action at VfL Bochum on Sunday.
- Deniz Aytekin
|1. FC Heidenheim 1846||13||3||2||8||-10||11|
|SV Darmstadt 98||13||2||3||8||-19||9|
|1. FC Union Berlin||12||2||1||9||-15||7|