1. A computer-implemented method of re-ranking sponsored search results by a search engine in response to a search query, the method comprising: retrieving, by a search engine, one or more organic search results and a plurality of sponsored search results (“search results”), along with their respective rankings, associated with a search query; determining, by the search engine, a degree of association between each sponsored search result and the other search results through analyzing web links between the plurality of sponsored search results, the one or more organic search results, and other web documents to or from which the search results are at least indirectly linked; calculating, by the search engine, a clustering score for each sponsored search result based on their respective degrees of linking association; generating, by the search engine, a new ranking score for each sponsored search result based on their respective clustering scores and rankings; re-ranking, by the search engine, the plurality of sponsored search results based on the new ranking scores of each respective sponsored search result; and storing in memory, by the search engine, the plurality of re-ranked sponsored search results in relation to the search query.
2. The method of claim 1 , further comprising: delivering the re-ranked plurality of sponsored search results to a user in response to the search query submitted by the user.