Yuya Osako struck twice during Cologne's 6-1 win away to Darmstadt in the Bundesliga on Saturday.
The Japan forward headed in Cologne's second in the 36th minute before making it a 4-1 game after 72 minutes, burying a shot into the bottom corner from outside the box.
Osako now has four goals for the season. Cologne is in seventh place with 29 points, 16 points off the pace of Bayern Munich.
Elsewhere, Osako's international teammate Gotoku Sakai opened his season account in Hamburg's 3-1 defeat to Ingolstadt.