(REUTERS) - An estimated 71.6 million people watched the final debate between White House contenders Hillary Clinton and Donald Trump on TV on Wednesday (Oct 19), below the audience for their first encounter but the third-largest total ever recorded.

The data supplied by the Nielsen ratings agency on Thursday (Oct 200 covered people who watched Wednesday night's debate on the four main US broadcast networks plus nine cable and public television channels.

The first Clinton-Trump face-off in September attracted a total TV audience of 84 million, the largest in the history of US presidential debates.

Last week's second debate, which was broadcast opposite popular Sunday Night Football, was seen by 66.5 million.

Wednesday's audience ranked as the third-highest for a US presidential debate since Nielsen started collecting TV viewership figures for the encounters in 1976. A 1980 debate between Democratic President Jimmy Carter and Republican challenger Ronald Reagan drew 80.6 million viewers.

Nielsen data reflects only those who watched the debate on TV at home and did not include millions more who watched online, through social media or in bars and restaurants.

The third debate ahead of the Nov 8 election was marked by Trump's refusal to commit to accepting the outcome of the election if the Republican candidate loses to his Democratic rival, challenging a cornerstone of American democracy.

The presidential election debate, held in Las Vegas, was moderated for the first time by a journalist from Fox News, Chris Wallace. It gave Fox News cable channel the lead in number of viewers for the debate at 11.2 million, followed by broadcasters ABC and NBC with more than 10 million viewers each.

Second and third presidential debates have generally attracted smaller TV audiences because many voters have already made up their minds after a presidential campaign lasting more than a year.