Eleven TV networks carried Wednesday night's debate live. Telemundo showed it on tape delay.
Nielsen says you have to go back to the second debate involving Bill Clinton, George Bush and Ross Perot in 1992 for a more popular presidential debate.
Four years ago the vice presidential debate between Joe Biden and Sarah Palin attracted 69.9 million viewers.
Nielsen says 11.25 million people watched the debate on ABC, 11.07 million watched on NBC, 10.58 million on CBS, 10.44 million on Fox News Channel, 6.88 million on the Fox broadcast network, 6.05 million on CNN, 4.73 million on MSNBC and 2.58 million on Univision.