Maximilian Marterer gave a weakened Germany team the advantage in their Davis Cup group opener with Slovakia in China on Tuesday. The 29-year-old beat Lukas Klein 6-4, 7-5 at the Hengqin International Tennis Centre in Zhuhai. “I think it’s a big relief for us,” Marterer said. 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 game of the match and did not look back. In addition to Slovakia, Germany face Chile and the US for one of the top two place…