New York (CNN Business) Thursday night's Democratic debate featuring Kamala Harris, Joe Biden, and eight other candidates was the highest-rated Democratic match-up in Nielsen ratings history.

Nielsen NLSN About 18.1 million viewers tuned in for the debate across three TV channels — NBC, MSNBC and Telemundo — according todata.

The previous record for a Democratic debate was set in October 2015, when 15.5 million viewers tuned in to CNN for the first primary season debate between Hillary Clinton and Bernie Sanders.

As political experts expected, Thursday's debate sparked even more interest, likely because the highest-polling candidates were on stage together for the first time.

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