Aug 25 (Reuters) - A total of 15.8 million people watched the mostly virtual Republican National Convention's first night on Monday, according to early Nielsen Media Research, fewer than the 18.7 million viewers who watched the first night of the Democratic National Convention across the same number of networks.

The 15.8 million RNC number reflects the audience across six TV networks between 10 p.m EDT and 11 p.m. EDT and does not include online and streaming viewers. Fox News had the biggest audience, with 7.1 million viewers.

A total of 19.7 million people watched the first night of the virtual Democratic National Convention on 10 U.S. TV networks on Aug. 17. A comparable figure for the RNC is expected later on Tuesday.

The Republican convention's first night featured speeches by former U.N. Ambassador and former South Carolina Governor Nikki Haley; Donald Trump Jr., the president’s oldest son; and Mark and Patricia McCloskey, the St. Louis couple who pointed guns at Black Lives Matter protesters who marched past their home.

Most of the speakers appeared in a virtually empty auditorium in Washington, bowing to the reality of the pandemic despite President Donald Trump’s push for a big event in front of thousands of admirers.

In making their case for Trump's re-election on Nov. 3, many speakers portrayed the United States as a country on the verge of chaos, arguing that the election of Democrat Joe Biden would lead to radical socialism and restrictions on Americans' freedoms.

Democrats had a bigger audience on the first night of the 2016 conventions as well. The first night of the 2016 Republican National Convention in Cleveland attracted 23 million viewers. That year’s Democratic National Convention in Philadelphia attracted 26 million viewers on its first night. (Reporting by Helen Coster; Editing by Leslie Adler and Jonathan Oatis)