Google launched a five-day court battle against European Union antitrust regulators in an attempt to annul a $5 billion fine it received over alleged anti-competitive behavior.

The battle is Google's attempt to revert the 2018 fine that condemned the tech giant for controlling its Android mobile operating system. The EU Commission says the company is promoting its own apps and services rather than allow other services to thrive but Google’s lawyers plan to point fingers at Apple, arguing that regulators failed to take their rival into consideration. 

During the hearing, Google’s lawyer Meredith Pickford told the court that “the Commission shut its eyes to the real competitive dynamic in this industry, that between Apple and Android.” 

“By defining markets too narrowly and downplaying the potent constraint imposed by the highly powerful Apple, the Commission has mistakenly found Google to be dominant in mobile operating systems and app stores, when it was in fact a vigorous market disruptor,” he said.

Android is the leading mobile operating system worldwide as of June, controlling about 73% of the market, according to Statista. Google’s Android and Apple’s iOS control over 99% of the global market share combined.

"Android has created more choice for everyone, not less, and supports thousands of successful businesses in Europe and around the world. This case isn't supported by the facts or the law," Google said at the hearing. 

EU Commission lawyer Nicholas Khan told the court that “bringing Apple into the picture doesn’t change things very much. Google and Apple pursue different models.” 

Khan noted that Google forces phone manufacturers to pre-install Google Search, the Chrome browser and the Google Play app store on their Android devices.

A verdict on Google is expected next year.

Google has already made a few changes to its Android system, including giving European Android users a choice of browser and search app, and charging device makers to pre-install its apps, NPR noted.

Google and Apple are the world's biggest tech companies. Google (GOOG), a subsidiary of Alphabet Inc., has a market cap of about $1.9 trillion. Apple (APPL) has a market cap of $2.4 trillion.