Maximilian Marterer and Yannick Hanfmann helped a weakened Germany team to a 3-0 victory in their Davis Cup group opener with Slovakia in China on Tuesday. The 29-year-old Marterer beat Lukas Klein 6-4, 7-5 in the first rubber at the Hengqin International Tennis Centre in Zhuhai. “I think it’s a big relief for us,” Marterer said. “I’m very happy with this start to the week, it makes me want more.” In extremely humid conditions, the left-hander kept his concentration and exploited the weaker serve of world number 128 Klein. Marterer, ranked 104th in the world, managed a break in the very first …