Do I need a visa to play in the WSOP?

I plan to participate in the upcoming WSOP. This would be the first time I enter the US. I live in an ESTA-eligible country, which means that I can apply for the Visa Waiver program online and visit the US without a visa. However I am concerned that the possibility of generating income from the event (although I don't think I will be in the money) disqualifies me from ESTA, or means that an ESTA alone would not be enough.

Am I worrying about a nonexistent problem? Is an ESTA enough to guarantee entry into the US for the WSOP? If not, is the standard B-1/B-2 visa sufficient?