Cursor Fix on the keeper. Then change the camera view to 'Keeper 3', focus on the ball or the GK (not using Player Cam), then timng is everything here. Once you feel that the keeper can snatch the ball away from the dribbler, move the keeper towards the ball, and press square (I think the save is automatic if you have good positioning, but I pressed square, and that won't hurt). Try it, it is the easiest move you can try. But try it on a friend first.