Amazon seems to have established itself in such a way that is giving direct competition to Google in the US. The online search advertising in the US is now divided between Amazon and Google. Read more at ibtimes.com
Apart from Google, small players including Amazon, Walmart, Target , eBay and Pinterest have witnessed growth in their shares. Amazon overtime has seen quite improvement with the introduction of new and better targeting tools.
Google may be dominating currently but the future years might see Amazon taking the dominant position.