Bayer Leverkusen's march to a historic maiden Bundesliga title continued after a hard-fought 2-1 win at home to Mainz.
In-demand Xabi Alonso saw his side take an early lead after former Arsenal captain Granit Xhaka scored with a stunning arching shot on the edge of the area.
However, the home side were quickly pegged back in the seventh minute when Dominik Kohr headed past Lukas Hradecky.
That set up a nervy second period after Leverkusen had squandered a series of golden opportunities to retake the lead.
But just after the hour mark their dominance was rewarded from Robert Andrich's speculative strike from range.