A total of 18.1 million viewers tuned into NBC News, MSNBC and Telemundo combined for Thursday night's Democratic presidential debate.

The figures make the event the second most-watched primary debate in television history and the largest on the Democratic side.

According to Nielsen Fast National Data, the event in Miami was also the second most-watched in the 25-54 demographic that advertisers covet, attracting 5.3 million viewers.

A majority of the viewers tuned to NBC on the broadcast side compared to cable channels MSNBC and Telemundo.

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Ten candidates appeared in the debate, which grew fiery after Sen. Kamala Harris Kamala HarrisHundreds of lawyers from nation's oldest African American sorority join effort to fight voter suppression Biden picks up endorsement from progressive climate group 350 Action 3 reasons why Biden is misreading the politics of court packing MORE (D-Calif.) went after Joe Biden's record on civil rights. The former vice president has been the front-runner in the race, leading all national polls since launching his campaign in April.

Sen. Bernie Sanders Bernie SandersThe Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power Bernie Sanders: 'This is an election between Donald Trump and democracy' The Hill's 12:30 Report: Trump stokes fears over November election outcome MORE (I-Vt.) and South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBillionaire who donated to Trump in 2016 donates to Biden The Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November Buttigieg stands in as Pence for Harris's debate practice MORE (D) also appeared in the debate, along with six other candidates. The event came on the heels of another Democratic debate featuring 10 other White House hopefuls the previous night.

Both debates were moderated by "NBC Nightly News" anchor Lester Holt, "Today" show co-host Savannah Guthrie, "Meet the Press" moderator Chuck Todd Charles (Chuck) David ToddMurkowski: Supreme Court nominee should not be taken up before election Republican senator says plans to confirm justice before election 'completely consistent with the precedent' Sunday shows - Trump team defends coronavirus response MORE, MSNBC host Rachel Maddow Rachel Anne MaddowGOP lawmakers distance themselves from Trump comments on transfer of power Schiff urges Trump administration members to resign: 'You cannot maintain your silence' Michael Cohen: Trump hates Obama because he's everything he 'wants to be' MORE and "Noticias Telemundo" and "NBC Nightly News" Saturday anchor José Díaz-Balart.

The most-watched primary debate in history occurred in August 2015 in the lead-up to the 2016 presidential election, when more than 24 million people tuned in to Fox News for the GOP event in Cleveland, Ohio.

That debate, which featured Donald Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE as a candidate for the first time, also attracted a record 7.9 million viewers in the 25-54 demographic.

The first debate on the Democratic side in the 2016 campaign season occurred in October 2015, when 15.5 million viewers tuned into CNN for an event that featured former Secretary of State Hillary Clinton Hillary Diane Rodham ClintonFox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio Trump, Biden court Black business owners in final election sprint The power of incumbency: How Trump is using the Oval Office to win reelection MORE and Sanders.