The US government has gone back to basics in arguments against Alphabet's Google, wrapping up the evidentiary phase of a court battle in which it has accused the online search leader of breaking antitrust law with its tactics.
In the trial, which started on September 12 and is widely expected to end on Thursday, the Justice Department is seeking to prove that Google is a monopolist and illegally abused its power to favour its bottom line.
Judge Amit Mehta of the US District Court for the District of Columbia will decide the case, the first of four aimed at reining in tech leaders.
The government has filed a second case against Google as well as one each against Meta and Amazon.com.
MIT economics professor Michael Whinston, the government's final witness, argued that Google's US market share of nearly 90 per cent meant it had little incentive to improve quality.
"When there's not a competitive threat, they're not making that investment. And quality is lower," Whinston said under questioning from Adam Severt of the Justice Department, one of the lawyers who signed the original 2020 complaint against Google.
Whinston disagreed with Google's arguments that it had to compete with Microsoft to be exclusively pre-installed on smartphones.
Google's payments to Apple and others, totalling $US26.3 billion ($A40.5 billion) in 2021, are essentially monopoly profits paid to distributors, he said.
"Google made a lot of profit on these contracts."
Alphabet reported a net profit of $US19.69 billion for July to September, up from $US13.91 billion in the year-ago period.
Revenue totalled $US76.69 billion for the quarter.
"Google has exercised significant market power by raising prices. It has done so to capture as much of advertisers' surplus as it can," said Whinston, citing Google experiments showing advertisers had little reaction when it raised ad rates.
"Every time, they found that raising prices is profitable."
Witnesses from Verizon, Samsung and Google itself have previously testified about the company's annual payments to ensure that its search is the default on smartphones and browsers and to keep its market share in the stratosphere.
No decision on whether to hold closing arguments, the final phase of the trial, has been made.