(Reuters) - The U.S. Department of Justice will make its final argument on Monday that Google illegally dominated online advertising technology, seeking a second antitrust win against the company.

The closing arguments in Alexandria, Virginia, cap a 15-day trial held in September where prosecutors sought to show Google monopolized markets for publisher ad servers and advertiser ad networks, and tried to dominate the market for ad exchanges which sit between buyers and sellers.

Google has argued prosecutors are bending U.S. antitrust law to force it to accommodate competitors' services, and that the case is focused on incidents from years past when Google was still building and improving its offerings. 

Publishers testified at trial that they could not switch away from Google, even when it rolled out features they disliked, since there was no other way to access the huge advertising demand within Google's ad network.

News Corp in 2017 estimated losing at least $9 million in ad revenue that year if it had switched away, one witness said.

If U.S. District Judge Leonie Brinkema finds that Google broke the law, she would consider prosecutors' request to make Google at least sell off Google Ad Manager, a platform that includes the company's publisher ad server and its ad exchange.

Google offered to sell the ad exchange this year to end an EU antitrust investigation but European publishers rejected the proposal as insufficient, Reuters first reported in September.

Analysts view the ad tech case as a smaller financial risk than the case where a judge ruled Google maintains an illegal monopoly in online search, and where prosecutors have argued the company must be forced to sell its Chrome browser.