Move over, Google: the latest version of Apple’s iOS search assistant, Siri, uses Microsoft’s Bing for searches.

Eddy Cue, senior vice president of Internet Software and Services for Apple, showed off the Bing integration as part of the announcements at its Worldwide Developer Conference (WWDC) on Monday, inserting it into the discussion without fanfare.

Apple alliance looks like a win for Microsoft

While that revelation may be a small one compared to Apple’s other WWDC announcements — iOS 7, OS X “Mavericks”, and a refreshed MacBook Air, among others—it's a big one for Microsoft, which has significantly trailed Google in terms of overall search share. In April, about 66.5 percent of U.S. searches were performed using Google’s sites, compared to 17.3 percent for Microsoft, according to comScore. Historically, Siri has defaulted to Google, although you could still order it to search via Bing or other search providers.

But if Microsoft can’t win by competing directly against Google, its new strategy could be to flank it: The company has inked search deals with Yahoo, and Bing is the search engine for Facebook’s Graph Search as well. It’s too early to tell whether the deals are paying off, as Microsoft continues to report losses within its online division, albeit decreasing ones. Research firm comScore reported that Microsoft’s U.S. search share is now 17.3 percent, up almost half a percentage point from a month ago.

Bing gets second priority in searches

However, Microsoft’s role in its relationships with Apple and Facebook is essentially a backstop. If Facebook can’t supply an answer to a query itself, it defaults to Bing, and Microsoft can serve up its own results. As an example, a user can search for “friends that live in Chicago,” and Facebook will generate a list of the user’s friends that live in the Windy City. But if Facebook can’t answer the query, “where can I eat in Chicago, ” those results are fulfilled by Bing.

Because Apple and Facebook have a vested interest in making sure that those results aren’t lost to Bing, the arrangement seems designed to deliver a smaller share of searches to Microsoft over time. For example, one might think that the phrase “pizza restaurants in Chicago” might automatically refer a search to Bing. But Facebook taps into its own social graph, parsing it for references to pizza restaurants in Chicago, and returning results within its own context. Likewise, a search for “best pizza restaurant in Chicago” makes a recommendation based on its users’ Likes.

Microsoft's alliance with Yahoo remains fragile

Yahoo’s relationship with Microsoft is more direct, as Bing powers Yahoo’s search results. However, with Yahoo, Microsoft hasn’t been able to deliver the search traffic that Yahoo has contractually required. Microsoft guaranteed Yahoo’s revenue per search on its properties for 18 months after the transition of its paid search services to Microsoft’s platform. But Yahoo, although it signed an extension of the deal with Microsoft last month, reportedly hasn’t been happy with the deal and has sought a way out.

Nevertheless, a Bing-Siri deal, as well as future integrations with search-like services, could mean that Microsoft slowly gains share over time. It's a strategy worth watching.

Correction: One of the search metrics was misattributed to Google. It should have been attributed to comScore.