Google (GOOG) widened its lead as the world's most popular search engine last month as students returned to school. The company attracted 66.1% of U.S. searches in September, up from 65.4% the previous month, according to a ComScore report released Wednesday.

The gain marked the first month-over-month increase this year for Google, which is scheduled to report its third-quarter earnings Thursday, UBS analyst Brian Pitz wrote in a research note.

Meanwhile, the search share for Yahoo, the No. 2 search engine, fell to 16.7% in September from 17.4% in August, according to ComScore. Microsoft Corp. (MSFT), Ask Network and AOL Network sites collectively accounted for 17.2% of search-engine visits in September, remaining approximately flat from August, ComScore said.