After all the hype over the new racially divided tribes on “Survivor: Cook Islands,” the ploy didn’t perk up numbers for the long-running CBS reality show. In fact, it had its lowest-rated debut in years.

“Survivor” averaged a 6.3 adults 18-49 rating last night, according to Nielsen overnights, down 10 percent from last spring’s 7.0 for the debut of “Survivor: Panama-Exile Island” and the lowest-rated premiere in at least the last five cycles of the show.

Though “Survivor” dominated the hour, nearly equaling the combined averages of CBS, Fox and ABC, it faced only two originals. Next week, when NBC returns its cult hits “My Name is Earl” and “The Office” in the 8 p.m. timeslot and ABC premieres the highly touted “Ugly Betty,” “Survivor” should still win the timeslot but perhaps with a lower rating.

Among total viewers, the show averaged 17.7 million, down 8 percent from last year’s 19.3 million.

Earlier this summer, CBS announced that this edition of “Survivor” would split the tribes into four groups according to race: whites, blacks, Asians and Hispanics.

The move drew protests from some minority groups and disdain from many “Survivor” fans, who wondered just how desperate for ratings the show had become.

CBS called the move a sociological experiment, but it was clearly sparked by declining ratings for the once-dominant franchise, which last spring had its lowest average ever among total viewers, dipping below 17 million.

Still, “Survivor” fared much better than week two of the new Fox sitcom “’Til Death,” also at 8 p.m. A week after debuting respectably against the highly rated NBC NFL opener, “Death” declined by 20 percent, averaging a 2.4 to last week’s 3.0. The show, which received mixed reviews, stars “Everybody Loves Raymond’s” Brad Garrett.

“Survivor” helped CBS win the night among adults 18-49, averaging a 5.3 rating and 16 share, followed by ABC at 3.0/9, Fox at 2.2/7, NBC at 2.1/6, Univision at 1.7, and the WB at 0.7.

At 8 p.m., “Survivor” was No. 1 with a 6.3, followed by ABC’s “Grey’s Anatomy” repeat at 2.4, Fox’s “Death” (2.4) and “Happy Hour” (2.1) at 2.2, NBC’s two “Earl” repeats at 2.0, Univision’s “La Fea Mas Bella” at 1.8, and the WB’s “Smallville” repeat at 1.6.

At 9 p.m., CBS kept the lead with a 4.8 for a “CSI” rerun, followed by ABC’s “Grey’s” rerun at 3.4, NBC’s “Earl” and “Office” reruns at 2.4, Fox’s “Celebrity Duets” at 2.3, Univision’s “Barrera de Amor” at 1.8, and the WB’s “Supernatural” repeat at 0.6.

At 10 p.m., CBS’s “CSI” rerun led at 4.7, followed by ABC’s “Primetime” at 3.3, NBC’s “ER” rerun at 2.0 and Univision’s “Aqui y Ahora” at 1.5.

Among households, CBS led at 10.0/7, followed by ABC at 5.7/10, Fox at 3.9/6, NBC at 3.5/6, Univision at 2.2/4 and the WB at 1.1/2.