Lawyers for the government have revealed damning Google correspondence and called witnesses who describe anti-competitive practices. Google, however, says ‘there is no monopoly power.’

Regulators contend that Google built, acquired and maintains a monopoly over the technology that matches online publishers to advertisers.

Google has opened its defense against allegations that it holds an illegal monopoly on online advertising technology with witness testimony saying the industry is vastly more complex and competitive than portrayed by the federal government.

The antitrust lawsuit comes a month after a federal judge declared that Google's search engine was an illegal monoply.

The government on Friday concluded its main arguments in the case -- US et al. v. Google -- and the internet giant started mounting its defense. The case, filed last year, accuses Google of building a monopoly over the technology that places ads on websites around the internet.