The first presidential debate between Democrat Hillary Clinton and Republican Donald Trump drew 84 million US television viewers, a record for such an event and numbers rarely seen on TV in the age of digital streaming and social media.
The audience for the night face-off beat the 1980 record of 80.6 million set by the Jimmy Carter-Ronald Reagan presidential debate, when viewers had far fewer entertainment options. But it fell short of the 100 million viewers some analysts had predicted.
The estimated ratings figure from Nielsen included people who watched the raucous encounter across 13 US cable and broadcast networks and public television station PBS.
The TV figures did not include millions of people who watched the debate online through Twitter, Facebook and other social media, including in large groups in bars and restaurants.
Alphabet Inc's YouTube reported nearly 2 million live concurrent streams of the debate on its platform.
The National Football League's annual Super Bowl attracts more than 100 million viewers, making it the biggest US TV event.
The debate was the first of three scheduled between Clinton and Trump before the November 8 election. The other two are set for October 9 and 19.
Fox News Channel grabbed the biggest cable audience with an average 11.4 million viewers, early Nielsen data showed. NBC, whose Nightly News anchor Lester Holt moderated the contentious exchanges about race, the economy and national security, was first overall with an estimated audience of 18.2 million.
TV networks had promoted the debates for days beforehand and reported strong demand compared with four years ago for commercial time during pre- and post-debate programming. Ad rates were far higher than for typical news programming.
CNN charged more than $US55,000 ($NZ75,000) for 30-second ad spots as part of packages ranging from $800,000 to $1 million that included future debates and election night, according to a person with knowledge of the matter.
CBS charged between $200,000 to $225,000, according to another source.
Both CNN and CBS have limited availability left for the next debate on October 9, the sources said.
"Clearly the debate did really well last night," said Michael Law, managing director of video investments at Dentsu Aegis Network.
Law said he did not expect ad rates for the next debate would rise significantly based on the night's audience. The Oct. 9 face-off airs against an NFL matchup of two popular teams - the Green Bay Packers and New York Giants.
"The NFL will likely do well on that night, but will probably see some fall-off during the 90 minutes of debate," Law said.
