But the Scottish champions fought back to defeat an in-form Stuttgart side who were at full strength after influential defender MarceloBordon appeared despite pre-match fitness fears.
Schalke failed to take advantage of Leverkusen's lapse despite extending their unbeaten run to seven matches, as MarceloBordon controversially had a goal disallowed soon after halftime when his header hit the underside of the crossbar and appeared to cross the line.