Complex sentence: Because of Kikumaru's knowledge about how to seal "Shukuchihou" from the match between Kai and Saeki, he easily takes the first games; then, Kai reveals that he's actually lefthanded and can use the racket backwards.
Split into simpler sentences: Because of Kikumaru's knowledge about how to seal "Shukuchihou" from the match between Kai and Saeki he easily takes the first games. At that time Kai reveals that he's actually lefthanded and can use the racket backwards.