The difference is that now your dog is moving to the disk, rather than having it come to him. If he catches it, praise him. Then gradually extend the distance on subsequent tosses. Don't Be Cruel. If your dog catches the disk and won't return it, don't punish him.
Dogs love to play keep-away.
Instead, fasten a rope or cord to his collar and hang on to the other end. Then reel him in and praise him. Be careful not to throw the disk farther than the length of your dog's cord or his neck could be jerked back before he can catch the disk. Eventually, you can coax your canine to leap for the disk with the single-mindedness of Dennis Rodman skying for a basketball. Do so by holding the disk over his head.