The blockbuster trial between Epic Games and Apple got off to a heated start in a federal courthouse in Oakland on Monday. Fortnite maker Epic opened by showering allegations on Apple, accusing the tech giant of turning its online marketplace into a monopoly. 

The Epic attorney started by saying that Apple has created a monopoly 'walled garden' that lures in developers and users and then squeezes money out of them.

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"Apple essentially planted a flower in the walled garden (that) was turned into a Venus flytrap," the lawyer said as per AFP. She further added that the iPhone makes profits of as much as 78% from apps.

"The evidence will show unambiguously that Apple is a monopoly," she claimed.

Firing back, Apple's attorney said that Epic's suit is part of a "self-proclaimed war against mobile platform fees" that defies the law and the facts.

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"Apple is no more a monopoly than is a grocery market that sells a broad array of goods, competing with other shops, she added.

The attorney continued her defense by saying that Apple did not create a secure and integrated ecosystem to keep people out, it did that so it could invite developers in -- without compromising the privacy, reliability and quality consumers wanted.

If Epic prevails, she said , "The result for consumers and developers will be: Less security. Less privacy. Less reliability. Lower quality. Less choice. All of the things the antitrust laws seek to protect."

Epic, maker of the popular "battle royal" game Fortnite, is aiming to break the iPhone maker's grip on its App Store.

Epic's chief executive Tim Sweeney, the first witness, said Apple's actions forced his company to either accept unfavorable terms or lose the massive base of iPhone users.

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"As Fortnite scales beyond gaming... it is essential to include the more than one billion iPhone users," Sweeney said in his testimony.

Asked why he waited until now to file suit, he said, "It took me a very long time to come to the realization of all the negative impacts of Apple policies."

The trial resuming on Tuesday before District Court Judge Yvonne Gonzalez Rogers comes with Apple feeling pressure from a wide range of app makers over its control of the App Store, which critics say represents monopolistic behavior.

The two firms are debating whether Apple has the right to set ground rules, control payment systems and kick out apps from its marketplace that fail to comply. Also at stake is Apple's slice of revenue from iPhone apps of as much as 30%.

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Sweeney testified that Epic provoked a public confrontation with Apple by hiding a "Hot Fix" in a Fortnite app to bypass the iPhone maker's payment system in violation of a contract.

"I wanted the world to see that Apple exercises total control over availability of all software on iOS," Sweeney said.

A key element of Apple's business model is at stake in the case, said Tejas Narechania, a University of California law professor.

"It's going to tell us a lot about how we structure industries and the technology industry going forward," he said.

"Which is how tightly can companies like Apple and Amazon and Google, how tightly can they vertically integrate their products?"

Analyst Dan Ives at Wedbush Securities called the case a "Game of Thrones court battle," with Epic looking to bypass the app platforms of both Apple and Google "while trying to gain support from other developers/app makers in a 'groundswell movement'" against Apple.

But Ives said Apple has a strong defense.

"Apple has successfully defended its App Store moat again and again, with this time being no different in our opinion," Ives said in a research note.

Epic, which is seeking to return to the App Store without being forced to use Apple's payment scheme, is not alone in its criticism.

The European Union has formally accused Apple of unfairly squeezing out music streaming rivals based on a complaint brought by Sweden-based Spotify and others, which claim the California group sets rules that favor its own Apple Music.

A recently formed Coalition for App Fairness, which includes both Spotify and Epic, have called for Apple to open up its marketplace, claiming its commission is a "tax" on rivals.

Apple booted Fortnite from its online mobile marketplace last year after Epic dodged revenue sharing with the iPhone maker.

Apple does not allow users of its popular devices to download apps from anywhere but its App Store, and developers have to use Apple's payment system, which takes its cut.

Due to the legal row, Fortnite fans using iPhones or other Apple devices no longer have access to the latest game updates.