FILE PHOTO: U.S. Senator Elizabeth Warren speaks as former HUD Secretary Julian Castro, U.S. Senator Cory Booker, former U.S. Rep. Beto O'Rourke and Senator Amy Klobuchar listen during the first U.S. 2020 presidential election Democratic candidates debate in Miami, Florida, U.S., June 26, 2019. REUTERS/Mike Segar/File Photo

(Reuters) - The first U.S. Democratic presidential debate, a faceoff without the party’s frontrunners, hauled in a surprisingly large 15.3 million viewers across three television networks, according to Nielsen estimates released by NBC News on Thursday.

Wednesday’s debate among Elizabeth Warren, Beto O’Rourke and eight other candidates vying for the Democratic nomination for U.S. president aired live on Comcast-owned broadcaster NBC, cable channel MSNBC and Spanish-language network Telemundo. It was the most-watched event on U.S. television on Wednesday.

A second debate featuring 10 other contenders including Joe Biden and Bernie Sanders, the candidates who are leading in opinion polls, will run on the same networks on Thursday night.

Wednesday’s TV audience did not reach the all-time primary record set in 2016 when 24 million viewers tuned in for the first performance by Donald Trump in a Republican candidates’ debate on Fox News Channel.

Still, it far exceeded predictions from many analysts who said they expected interest would be limited so early in the election cycle and without a brash personality like Trump.

The audience matched the preliminary estimate of 15.3 million viewers for a Democratic debate in October 2015 on CNN, now owned by AT&T Inc. That number was later revised to 15.8 million, a record for a Democratic primary field.

In the surprisingly heated debate on Wednesday, several of the lesser-known Democrats candidates vied for attention in the crowded race to take on Trump in the 2020 election. Candidates sparred on topics including healthcare and border policy.

More than 9 million additional viewers watched Wednesday’s debate via live streams on the internet, NBC said.