Washington, DC - Google CEO Sundar Pichai faced a fierce grilling from a US antitrust lawyer on Monday as he pushed back against accusations that his company acted illegally to preserve the dominance of its world-leading search engine.

At the heart of the case by the US Department of Justice is Google’s massive revenue-sharing deals in which iPhone maker Apple takes a big cut of Google ad revenue made from being the default search engine on Apple devices.

Testimony has revealed that last year alone Google paid out $26 billion to remain the default search engine on various smartphones and browsers, most of which went to Apple.

Pichai began his testimony in the Washington courtroom by repeating the company's mission of making information "universally accessible and useful" to all.

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"The mission is more timeless and relevant than ever before," Pichai said, given new competitors for search and the advances in artificial intelligence.

But in two hours of questioning, the United States government antitrust lawyers tried to pick that claim apart.

Using company emails, chats, and letters that were sometimes two decades old, the government pushed Pichai to admit that Google's default arrangement with Apple was existential to its business.

In one tense back and forth, Pichai was presented with an internal memo in which Google expressed concern that some searches on Apple devices were being "cannibalized" by the iPhone's Siri.

In 2019, Pichai explained to Apple CEO Tim Cook that this could explain Apple's less-than-expected revenue from Google searches the previous year and could be fixed.

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"Our vision is that we work as one company" when it comes to search, a Google memo said, summarizing another high-level meeting between the two companies in 2018.

When shown the internal memo, Pichai insisted that the two tech giants "fiercely compete on so many products," while adding that "there was maybe some irrational exuberance on how well the meeting went."

Pichai was also needled about company chats where he asked that the conversation be switched to "history off" so that the content would be automatically deleted after 24 hours.

The use of the function has raised suspicion among the US government lawyers that Pichai had attempted to prevent incriminating conversations from being brought into evidence.