Bundesliga leaders Union Berlin again proved their season start is no fluke as they easily beat supposed title challengers Borussia Dortmund 2-0 at home on Sunday. Champions Bayern Munich replaced opponents Freiburg in second spot, four points behind Union, after Serge Gnabry, the impressive Eric Maxim Choupo-Moting, Leroy Sané, Sadio Mané and Marcel Sabitzer sealed a 5-0 romp at the Allianz Arena. Union took an early lead after Dortmund keeper Gregor Kobel slipped when trying to clear and presented Janik Haberer with the easiest goal he will ever score. More poor play from Dortmund’s backline…