US would get clobbered by india and china
I highly doubt that China would be able to beat the U.S. At least any time soon. Granted this is all theoretical anyway. China's education system is not by any means exceptional. For a nation at it's status of development, it is phenomenal, and the high population leads to an abundance of prodigies, however it is not a team of individuals selected from all over the nation, it is a team of one school.
This doesn't mean I don't think the U.S. wouldn't be destroyed by others. France and Japan would probably clean up. India is iffy, their education system is poor, however I would not be surprised if they have some exceptional centralized national schools. The United Kingdom would probably also do fairly poorly in comparison to the U.S. because of their relatively poor education system. Sweden would be a big player. Iran would as well, mostly due to the training of young physists for obvious reasons.
On second thought, China actually would probably destroy us as well, if only because of Hong Kong.