Regulators at the Federal Trade Commission (FTC) had been investigating complaints from Google’s rivals about its dominance of the internet search industry.
An internal report obtained by the paper showed that some FTC officials had wanted to prosecute.
Instead, the regulator persuaded Google to change the way its software worked.
Google said the “exhaustive” review showed there was no harm to competitors or consumers.
The FTC began its probe of the search market in 2011 following complaints from Google’s competitors.
During the investigation the regulator’s officials gathered nine million documents and obtained evidence from firms such as Yelp, TripAdvisor and Amazon, who had accused Google of taking content from their web pages.
The information Google gleaned was allegedly used by the firm to improve its own search ranking system.
The evidence gathered was enough to convince some FTC investigators that legal action should be taken, said the paper.
However when the regulator’s investigation ended, the agency concluded that the company had not abused its market position to hurt rivals.
Even so, the FTC arranged a deal with the company to end some of the practices that its rivals had complained about.
The report was inadvertently sent to the Wall Street Journal when it asked for details of a separate FTC investigation.
The agency has not commented on the accidental release of the report.
In a statement Google said: “After an exhaustive 19-month review, covering nine million pages of documents and many hours of testimony, the FTC staff and all five commissioners agreed that there was no need to take action on how we rank and display search results.”
It added: “Speculation about potential consumer and competitor harm turned out to be entirely wrong.”