It marked the end of an astonishing run where more than 40 million people watched political speeches on three nights by Obama, McCain and Republican vice presidential candidate Sarah Palin. The Republican convention was the most-watched convention on television ever, beating a standard set by the Democrats a week earlier.
Three times in two weeks, political speeches were watched by more people than the "American Idol" finale, the Academy Awards and the opening ceremony of the Beijing Olympics this year.
"It clearly suggests that a great number of Americans think that who will be the next president is important and worthy of their time," said Tom Rosenstiel, a former political reporter and director of the Project for Excellence in journalism.
Television ratings throughout the primary season had already indicated an intense interest in the election, but viewers clearly were more fascinated in the Democratic contest between Obama and Hillary Clinton than the Republican nomination fight.
This week's ratings, with an average of 34.5 million viewers watching the GOP convention over three days, proved people are becoming more interested in what the Republicans have to say. The Democrats had an average audience of 30.2 million over four days, Nielsen said.
"No one really thought they had it in them in terms of pulling off this amazing convention," said Jay Wallace, vice president for news and editorial at Fox News Channel. But Hurricane Gustav pulled people into the news networks over the weekend, he said. People were also intensely curious about McCain's pick of Palin as a running mate, he said.
Nielsen said that 38.9 million people watched McCain accept the GOP nomination Thursday on either ABC, CBS, NBC, CNN, Fox News Channel or MSNBC. PBS, which has a more imprecise estimate based on samples in a few big cities, said 3.5 million watched on its network.
Last week, Obama's speech in Denver was seen by 38.4 million on 10 different commercial networks, and an additional 4 million on PBS.
Add it up, and that's McCain, 42.4 million, to Obama, 42.4 million.
No one can really tell who truly had the biggest audience, since C-SPAN also showed the speeches, and Nielsen doesn't measure the cable channel's viewers. But if the presidential vote is this close on Nov. 4, it will be a long night.
McCain may have caught a break Thursday when the opening NFL game between the New York Giants and Washington Redskins finished a couple of minutes before the Republican took the stage, Wallace said.
More men (17.9 million) watched McCain speak than watched Obama (16.2 million), Nielsen said.
"The storylines this year have been so amazing," Wallace said. "It really got started with Hillary and Obama - that got everyone in middle America watching. They got caught up in the drama of it."
The numbers put to rest the thought that politics has been a turnoff and death for ratings, which has long been gospel at the TV networks, Rosenstiel said.
That has particularly applied to convention coverage, which broadcast networks have backed away from over the years because executives saw them as stage-managed events. ABC, CBS and NBC each added an hour this year to convention coverage, but it didn't halt one trend: Viewers are just as likely to watch the conventions on cable news networks.
Fox was the most-watched network all three nights of the GOP convention, duplicating its feat from the 2004 GOP convention. CNN was the most popular destination for Obama's speech.
Fox had 9.2 million viewers for McCain's speech, followed by NBC - which aired the football game - at 8.7 million. ABC, CBS, CNN and MSNBC followed in order, Nielsen said.
Thursday's edition of Fox's "The O'Reilly Factor," featuring the first part of Bill O'Reilly's interview with Barack Obama, was also the second-highest rated edition of his show ever, topped only by a night in March 2003 when the Iraq war was breaking out.