The Republican candidates' prime-time debate on Fox News Channel drew 24 million viewers, more than double the prior record for a presidential primary debate and the highest non-sports telecast in cable TV history, according to Nielsen data released on Friday.
The tally for Thursday's event in Cleveland more than doubled Fox News Channel's previous largest audience, the 11.8 million viewers who tuned in on election night in November 2012.
The brash style of billionaire real estate mogul Donald Trump, who dominated news coverage in recent weeks, and the large pool of candidates participating in the debate - 10 - had spiked interest.
Still, the size of the audience blew past predictions by media experts and provided a win for Fox News Channel, which is owned by Rupert Murdoch's 21st Century Fox.
Before Thursday, the most-watched primary debate was a 2008 event that included Democrats Hillary Clinton and Barack Obama. That telecast drew 10.7 million viewers.
Thursday's debate was just the first in a charged political season that will see one televised debate per month through the end of this year of the contenders for the Republican nomination for the November 2016 presidential election. The next Republican debate will be on Sept. 16, to be aired by CNN.
CNN will also host the first televised debate of the Democratic contenders, on Oct. 13.
Thursday's prime-time telecast drew 7.9 million viewers aged 25 to 54, the key group for advertisers on cable news broadcasts.
Fox aired 10 minutes of commercials during the two-hour telecast, from movie studios, carmakers and others, according to iSpot.tv, which tracks TV ads and digital responses. Advertisers included Sony Pictures, Verizon and Nissan Corp's Infiniti.
An earlier debate Thursday on Fox News Channel featured the other seven Republican candidates, whose low polling numbers kept them out of the prime-time debate. That debate averaged 6.1 million viewers.
While the audiences were large for cable, they ranked below the most-watched events on broadcast television. The Super Bowl in January attracted 114 million viewers, while February's Academy Awards pulled in 37.3 million.
Another TV event took place later Thursday on Viacom Inc's Comedy Central. The finale of "The Daily Show with Jon Stewart," where the comedian routinely skewered politicians and the news media, attracted 3.5 million viewers, its second-biggest audience, according to Nielsen data provided by the network.
(Reporting by Piya Sinha-Roy and Lisa Richwine; Editing by Leslie Adler)