The US government has accused Google of manipulating the ad tech market, stifling competition and innovation; the company recently lost an antitrust case targeting its search business.

A senior Google executive sought to refute the US Justice Department’s antitrust case over its display advertising technology business, testifying that it faces “fierce competition” from the likes of Microsoft Corp.

As the government wraps up its case, it has built a picture of how Google has become dominant among companies that buy and sell ads online.