Judges from the reality series "The X Factor" (L-R) L.A. Reid, Britney Spears, Demi Lovato and Simon Cowell are pictured on a video screen via satellite from Miami, Florida, during a panel discussion at the Fox television network portion of the Television Critics Association Summer press tour in Beverly Hills, California July 23, 2012.[Photo/Agencies]

"The Voice", NBC's singing contest, faltered with US TV viewers in its new fall slot, drawing smaller audiences among key viewers than its two previous season openers and setting an easy target for its rival on Fox, "The X Factor", when it returns later this week.

Early Nielsen data on Tuesday showed that 12 million Americans watched the two-hour season debut of "The Voice" on a night of tough competition with Fox and football.

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 for "The Voice" 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.

Nevertheless, "The Voice" trounced the finales of summer cooking shows "Hell's Kitchen" (6.2 million) and "Master Chef", (6.4 million), and the 10.9 million Americans who watched the Baltimore Ravens beat the Cincinnati Bengals on sports cable channel ESPN on Monday night.

The total audience for "The Voice" was also up on the 11.8 million who watched the contest finale in May.

NBC, which has been at the bottom of the four main US 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.