Mainz 05 secured a commanding 2-0 lead over Racing Strasbourg in their Conference League quarterfinal first leg after goals from Kaishu Sano and Stefan Posch.The German side dominated the opening stages at home with high intensity as Mike Penders prevented a heavier defeat for the French visitors.Strasbourg must now overturn the two-goal deficit in the return leg to reach their first European semifinal and potentially face Rayo Vallecano.