The Justice Department used its first full day of questioning in its antitrust trial against Google on Wednesday to establish that the internet giant had long sought agreements to be the default search engine on mobile devices, which the government argues were used to illegally maintain the company’s hold over online search.

Google responded by highlighting evidence suggesting that companies that signed those agreements — including smartphone makers, browser developers and wireless carriers — did so partly because its search product was better.

Chris Barton, a former Google employee who testified on Wednesday, said the company had been willing to pay mobile companies mainly to become their exclusive default search engine. “That’s the kind of primary goal of the partnership,” he said of the agreements.

The testimony came after the federal government’s first monopoly trial of the modern internet era kicked off on Tuesday. The Justice Department and a group of 38 states and territories have accused Google of illegally shutting out competitors and entrenching a monopoly over online search by using multibillion-dollar contracts with companies like Apple and Samsung to be the default search engine on smartphones.