Early Nielsen data on Tuesday showed that 12 million Americans watched the two-hour season debut of "The Voice."

That was enough to give NBC a Monday night win in both total viewers and in the 18-49 demographic coveted by advertisers.

But the third-season debut was down from a Super Bowl-fueled 17.7 million for February 2012's opener, and the 12 million was in line with "X Factor's" season average for 2011.

A drop for "The Voice" had been expected, but the 18 to 49- year-old audience was also smaller than in its two prior debuts.

NBC, which has been at the bottom of the four main U.S. networks for years, decided to program the contest twice a year, in the fall and the spring - risking viewer burn-out in a crowded field of TV talent shows.

Simon Cowell's "X Factor" returns on Fox on Wednesday with new judges Britney Spears and Demi Lovato, hoping to improve on last year's ratings performance.

"The Voice," with singers Christina Aguilera, Cee Lo Green, Adam Levine and Blake Shelton as judges, has been the brightest light in the NBC line-up since its debut in the spring of 2011.

NBC is majority-owned by Comcast. Fox is owned by News Corp.

(Reporting by Jill Serjeant; Editing by Gary Hill)

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