An estimated 25.1 million people watched the convention between 10 p.m. and 11 p.m. on Wednesday, when former President Bill Clinton delivered an impassioned nomination speech for President Barack Obama, the Nielsen ratings company said.

During that hour, just over 20 million people were watching the second half of the Dallas Cowboys’ season-opening victory over the New York Giants. Faced with competition from Clinton, ratings for football’s first game were down from the past two years.

The second night of the GOP convention in Tampa, Fla., last week, featuring vice presidential candidate Paul Ryan, was seen by 21.9 million people, Nielsen said Thursday.

Democratic convention ratings held up well compared to 2008, when interest was particularly high. The Democrats had a four-day convention then, with 25.9 million viewers on the second day and 24 million on the third. None of those nights faced competition from pro football.

The entire football game was seen by an average of 23.9 million people on NBC, Nielsen said. Last year’s opening game was seen by 27.1 million, and 2010′s game had a record 27.5 million. The opening game generally features the Super Bowl champion from the year before.

Competition among the TV networks televising the Democratic convention in Charlotte, N.C., on Wednesday was about as tight as polls show the presidential race between Obama and Republican Mitt Romney.

ABC had the biggest audience, with 4.59 million viewers. CBS had 4.41 million, MSNBC had 4.39 million, CNN had 4.13 million, PBS had 4.1 million and Fox News Channel had 3.1 million, Nielsen said.

Current TV and C-SPAN also showed the convention. Nielsen had no immediate estimate of Current’s viewership, and C-SPAN’s audience is not measured by the ratings agency.