ABC continues to struggle to find a good 10 p.m. companion for “Grey’s Anatomy” on Thursday night. While “Life on Mars” received strong reviews and a solid rating last week in its debut, last night the show lost much of that audience, even as “Grey’s” regained its dominance on the night.

“Mars” averaged a 2.7 adults 18-49 rating, according to Nielsen overnights, down 27 percent from a 3.7 in its debut last week. “Mars,” about a modern-day cop who finds himself transported back in time to 1973, retained only 47 percent of “Grey’s” 9 p.m. lead-in and finished third in the timeslot, behind NBC’s winning “ER” and CBS’s fellow new show “Eleventh Hour.”

Media people have said “Mars” has great creative promise, and certainly it will be some weeks before viewers are done sampling the different options in the hour. But “Mars” isn’t doing much better than a host of other failed dramas that have cycled through the post-“Grey’s” slot, including “Big Shots” and “Six Degrees.”

Still, DVR numbers could give the show a boost. Overnight ratings are based on live-plus-same-day DVR playback, and seven-day DVR data won’t be available for several weeks. Twenty-eight percent of Nielsen households have DVRs, and “Grey’s” gained 2.7 million viewers in its initial episode from DVR playback.

Speaking of “Grey’s,” the show regained its top spot on the night among 18-49s, a week after surrendering it to “CSI” for the first time. The latter slipped 28 percent from last week’s season-premiere 7.1 to a 5.1, while “Grey’s” was up a bit week to week to a 5.8.

NBC’s new sitcom “Kath & Kim” also declined from last week’s debut, from a 3.2 to a 2.5.

CBS finished first for the night among 18-49s with a 4.2 average overnight rating and an 11 share. ABC was second at 3.7/10, NBC third at 3.4/9, Univision fourth at 1.6/4 and Fox and CW tied for fifth at 1.4/4.
 
At 8 p.m. CBS led with a season-low 4.2 for “Survivor,” while ABC was second with a 2.6 for “Ugly Betty.” NBC was third with a 2.5 for “My Name is Earl” (2.6) and “Kim” (2.5). The CW and Univision tied for fourth at 1.7, CW for “Smallville” and Univision for “Cuidado con el Angel,” while Fox was sixth with a 1.4 for “Hole in the Wall.”
 
ABC took the lead at 9 p.m. with a 5.8 for “Grey’s,” followed by CBS with a 5.1 for “CSI.” NBC was third again with a 4.1 for “The Office” (4.1) and “Saturday Night Live Weekend Update” (4.1), Univision fourth with a 1.8 for “Fuego en la Sangre,” Fox fifth with a 1.4 for “Kitchen Nightmares” and CW sixth with a 1.2 for “Supernatural.”
 
At 10 p.m. NBC jumped to first with a 3.5 for “ER,” with CBS second with a 3.2 for “Eleventh Hour.” ABC was third with a 2.7 for “Mars” and Univision fourth with a 1.4 for “Rosa de Guadalupe.”
 
CBS also led the night among households with a 9.1 average overnight rating and a 15 share. ABC was second at 6.9/11, NBC third at 5.0/8, Fox fourth at 2.6/4, CW fifth at 2.2/3 and Univision sixth at 2.1/3.