A couple of Google’s chief rivals have just made significant hires that may help them better compete with the Internet giant.

Apple has hired William Strasior to run Siri, according to Kara Swisher at All Things D. Apple has already been making moves to improve Siri, and the hiring of Strasior has major implications for the direction Apple takes the product in.

With iOS 6, Siri gained the ability to understand more languages and it now works in more countries. It also added sports scores and stats, movie showtimes and reviews, and restaurant reservations. “Even have Siri open your apps for you — no tapping required,” Apple says on its website. “Say ‘Launch Flight Tracker’ or ‘Open Angry Birds’ and Siri does just that. You can also use Siri to post Facebook updates and tweet for you.”

Clearly, Apple was already designing Siri to take on Google in some areas, and these areas are sure to increase in number.

That’s where the hiring of Stasior gets interesting. He comes from Amazon where he was in charge of A9, Amazon’s search and advertising unit. Here’s what his resume (pdf) says about that:

A founder and now President / CEO of A9.com, a company with a mission to create groundbreaking technologies in search, advertising, and mobile that power customer centric, internet businesses. A9 is a fully owned subsidiary of Amazon.com, head quartered in Palo Alto, with roughly 200 employees and operations in Ireland, Germany, Romania, India, China, and Japan. A9 provides the core search service, as well advertising services, and image recognition technologies to Amazon.com and other websites. Prior to founding A9, led product and engineering for the Search & Navigation team at Amazon.

He used to work at AltaVista as the director of advanced development, where he worked on next generation search technologies.

With Apple’s giant user base, and recent trend of ditching Google products. This is going to be a very interesting narrative to keep an eye on, while certainly only helping Google’s argument against it being a monopoly.

Apple is not the only Google competitor to make a significant hire this week. Yahoo, now led by longtime, prominent Googler Marissa Mayer, just lured another noteworthy Googler away to fill the COO role at her company. That would be Henrique De Castro, who has been serving as Google’s President of Media, Mobile and Platforms Worldwide. So, that’s a pretty big position, and another blow to Google from Yahoo.

This is, by the way, only the latest in a series of Googlers who have jumped ship to join Mayer at Yahoo, which has been in the business of competing with Google since Google was invented – much longer than most of Google’s rivals.