Capitalism is a flawed system that leads to exploitation. There has been exploitation. In theory, capitalism makes some people very rich. From the second half of the 20th Century until now, China has pulled the USA into its pocket in financial terms. China pretty much owns America. Um... The End.
Capitalism is private ownership of the means of production (all non-human resources). Both the US and China have capitalist economies, but there appears to be more government seizure of private property in China than in the US. Still, the US does the same thing, it's called eminent domain, but China is the leader here.
Capitalism is a system that leads to the prosperity of its workers and citizens. If the hard work of the workers only benefits the elite few, then it is a corrupt and faulty system. The United States's system is hardly perfect, but at least has more choice, laws governing working conditions, and a minimum wage. Many jobs also have room for advancement, or educational opportunities. Our factories are not sweat shops. We have systems of health insurance and labor unions to protect workers' rights and safety.
First off, China is still a communist nation, so it is hard to consider it to have a capitalist economy to begin with. Also, China has a lot of very low paying jobs in sweatshops and the United States has a lot more prosperity with higher paying jobs. It is clear that the U.S. has a better capitalist system than China.
The answer to this very question is a simple one. China does not do capitalism better than the United States, because they do not use a capitalistic system. They use some kind of a hybrid market and government economy, that only uses some basic forms of the free market economy.