ABC has captured the opening Thursday of the season in key demos behind a two-hour “Grey’s Anatomy,” while NBC saw a potent premiere for “The Office” and CBS was competitive even without a firstrun “CSI.” No new shows bowed on the night, and all of the returnees posted declines.

According to preliminary nationals from Nielsen, “Grey’s Anatomy” (7.3 rating/18 share in adults 18-49, 18.3 million viewers overall) dominated the 9-11 p.m. block with its fifth-season premiere, even though it came in 17% below last year’s hourlong bow. It was the show’s best scores since last November, while its 18-49 result represented the best for any scripted series on any net since February.

Kicking off the night, “Ugly Betty” (3.3/9 in 18-49, 9.8 million viewers overall) ran second in most categories during the 8 o’clock hour and was off its year-ago pace by 15%. Still, it outperformed its final 10 episodes of last season.

At NBC, things started sluggishly with the hourlong premiere of “My Name Is Earl” (2.7/8 in 18-49, 6.4 million viewers overall) before picking up nicely at 9 p.m. with the hourlong opener of “The Office” (4.8/11 in 18-49, 9.2 million viewers overall). While “Earl” tumbled 29% from last year’s opener, “The Office” came within 6% of its year-ago debut score, which had tied for the show’s series high.

At 10, the 15th and final season premiere of “ER” (3.3/8 in 18-49, 7.9 million viewers overall) declined a hefty 20% from last year’s opener, no doubt impact by the extra hour of “Grey’s Anatomy.”

CBS went with a two-hour premiere of “Survivor,” which averaged a 4.4/11 in 18-49 and 12.9 million viewers overall, winning the 8 o’clock hour as usual and slipping to third in demos opposite tougher competition from 9 to 10. The veteran reality show was down about 12% from last year’s premiere, which aired one week before the season started. A repeat of “CSI” closed out the night (2.5/6 in 18-49, 9.4 million viewers overall), as the crime show’s season premiere is on tap for Oct. 9.

Fox had a quiet night with “Kitchen Nightmares,” first with a special additional hour at 8 (1.9/5 in 18-49, 4.2 million viewers overall) and then with its regular episode at 9 (2.1/5 in 18-49, 4.5 million viewers overall).

CW’s “Smallville” (1.7/5 in 18-49, 4.1 million viewers overall) held up well week to week, but lead-out “Supernatural” (1.3/3 in 18-49, 3.2 million viewers overall) took a dip vs. its premiere of last week.

Preliminary 18-49 averages for the night: ABC, 6.0/15; CBS, 3.8/10; NBC, 3.6/9; Fox, 2.0/5; CW and Univision, 1.5/4.

In total viewers: ABC, 15.5 million; CBS, 11.7 million; NBC, 7.8 million; Fox, 4.3 million; Univision, 4.0 million; CW, 3.7 million.