India, March 16 -- One of the great sporting rivalries will be renewed at Indian Wells on Saturday when Roger Federer and Rafa Nadal clash in a semi-final at the BNP Paribas Open, providing the Spaniard's troublesome right knee does not keep him off court.The multiple Grand Slam champions both won their quarter-finals on Friday, although Nadal in particular had to work hard to overcome Russian Karen Khachanov 7-6(2) 7-6(2) in a match during which he required treatment on the knee."I am used to playing with some issues, so I just tried to be focussed. It's one of these victories today I'm really proud of," Nadal told reporters, declining to absolutely guarantee that he would be okay to play on Saturday."Nobody can guarantee anything about wh...