Read more about sharing. Croatia's Marin Cilic won his first Grand Slam title with a comprehensive straight-sets win over Kei Nishikori of Japan at the US Open. Cilic won 6-3 6-3 6-3 to become the first Croat to win one of the four tennis majors since his coach, Goran Ivanisevic, at Wimbledon in 2001.