A lot of people seem to think that, even if China does advance faster than the USA in terms of economical development, it suddenly means that the USA are going to be completely blown out of the water. As much as we like it, the world doesn't run on a monopoly. At least not until a nation can manage to take over enough parts of the world to have a sufficient enough hold over various natural materials and resources, as well as labor and well-fare of their population. And without that you just have an unbalanced market. People might not like the idea of competition, but it's better than one guy deciding the prices and getting fucked over because no one else is selling what he has. Like what's going on in Zimbabwe. 

That and China isn't going to be doing well even if it can overcome the US in terms of economy. They got their own problems too. It just means they're losing money a bit slower than before, but still on a steady decline. They're going to need more than an economical lead to tip the balance. And that's assume that the development of the rest of the world remains stagnant and unchanging. Which is false if China is capable of gaining some sort of lead; someone else has to be failing, and that doesn't mean it's the USA. More likely it's going to be a neighboring country for the Chinese to exploit, like Laos or something.