Microsoft and Yahoo said today that they have completed the shift to using Redmond's AdCenter tools to power paid search in the U.S. and Canada on Yahoo and its partner sites.

"As of today, AdCenter powers 100 percent of paid search advertisements on both Bing and Yahoo!, partner sites and publisher networks in the U.S. and Canada," the companies said in a joint statement. It's part of the companies' massive 10-year deal aimed at joining forces in search to better rival market leader Google.

Although the companies had a goal of doing so by the end of this month, they had said they were willing to push things back so as not to interfere with business in the all-important holiday shopping season.

"The transition comes after months of testing and collaboration between Yahoo! and Microsoft, with strict attention being paid to protecting the quality of experience for publishers and advertisers during the upcoming holiday season," the companies said.

Yahoo made the shift to using Bing for organic (non-paid) search results in August.

The companies still plan to move Yahoo's mobile search advertising to Microsoft's engine by the end of October.

The international move will take more time, with the complete work not expected to be complete until early 2012. On the organic front, the companies plan to shift Spanish-speaking Latin America in the first quarter of next year. For paid search, the first countries will be the United Kingdom, France, Ireland, and India, which are slated for the second quarter.