RB Leipzig spoiled hosts Union Berlin's Bundesliga debut on Sunday, crushing the top division newcomers 4-0 with a performance that confirmed their pre-season title contenders tag. Marcel Halstenberg fired home from 20 metres in the 17th minute and then pounced on a keeper error to set up Marcel Sabitzer for the visitors' second goal in the 31st with only their second shot on target on a rain-drenched pitch in the capital. Forward Timo Werner completed a fine combination with a powerful shot to send Leipzig into the break with a three-goal cushion. Substitute Christopher Nkunku tapped in from close range in the 69th for their fourth goal after the visitors also twice hit the woodwork. Union, who lost only once at home in the second division last season, struggled with Leipzig's pace throughout and were unable to mount any serious attacks of their own. Eintracht Frankfurt edged past Hoffenheim 1-0 in the only other game on Sunday. Borussia Dortmund enjoyed a five-star premiere, crushing Augsburg 5-1 on Saturday, while champions Bayern Munich stumbled to a 2-2 draw against Hertha Berlin a day earlier.