Roger Federer. Pic/AFP

New world number one Roger Federer believes that last year's US Open "unlocked" something in big-serving South African tennis star Kevin Anderson. The 20-time Grand Slam champion said that Anderson's run to the finals of the last year's US Open might have unlocked the belief that he could finally win a major tournament. "I think the US Open might have unlocked a lot of things for Kevin in his head and in his game that maybe before he wasn¿t sure he could achieve," Sport24 quoted Federer as saying.