By Jill Serjeant and Lisa Richwine

NEW YORK/LOS ANGELES (Reuters) - The television audience for the second debate between White House contenders Donald Trump and Hillary Clinton fell sharply from their first, record-breaking encounter, despite the drama caused by a 2005 video of Trump boasting about groping women.

Nielsen data for 11 broadcast, cable and public television channels on Monday showed that some 66.5 million Americans tuned into the bitter 90-minute debate on Sunday, well below the record 84 million that watched the first face-off two weeks ago.

The figures do not include millions more who watched the debate online, through social media or in bars and restaurants.

Second presidential debates tend to attract smaller TV audiences, but attention was high going into Sunday's matchup after the emergence of the Trump video prompted several Republican politicians to abandon him.

However, the second debate took place in the same time slot as NBC's popular "Sunday Night Football," which was watched by about 15 million Americans, Nielsen data showed. NBC did not carry the debate.

While the National Football League game, along with Major League Baseball play-offs, likely pulled viewers away from the debate, many Americans already may have made up their minds on candidates, said Tom Hollihan, communication professor at the University of Southern California’s Annenberg School.

"When we get to mid-October, history tells us people have already made their decisions," he said. "They lock themselves into their viewpoints and are less open to new information."

The furor over the Trump tape and his attacks on Hillary Clinton's husband, former President Bill Clinton, for alleged sexual misconduct also may have turned off some viewers.

Sunday's debate, the second of three before the Nov. 8 election, was remarkable for the brutal nature of the exchanges between Trump and Clinton, his Democratic rival.

"While in the past families might have made a commitment to watch a presidential debate, I think many in this case were saying, 'Why should I do that? Why should I have to answer my kids’ questions about these topics?'" Hollihan said.

The TV audience ranked below the nation's top 10 most-watched presidential encounters, and below that for President Barack Obama's first and second 2012 debates with Republican challenger Mitt Romney.

Last week's vice presidential debate between Republican Mike Pence and Democrat Tim Kaine drew 37 million Americans - the lowest audience for a VP debate since 2000.

(Reporting by Jill Serjeant and Lisa Richwine; Editing by Bill Trott and Jonathan Oatis)