Undercover Boss's Friday 8pm dominance is under threat, according to Nielsen overnight data.
The CBS reality show fell to 8.6m, down 2.1m week-on-week and falling 21% to a rating of 1.9 in the adult 18-49 demos.
Meanwhile, ABC's Shark Tank climbed to 5.9m (1.8), Fox's Kitchen Nightmares had 3.5m (1.5) and Who Do You Think You Are? grabbed 5m (1.0) for NBC.
The Peacock Network led the 9pm hour with Grimm (4.8m/1.5), beating ABC's Primetime (4.6m/1.4), CBS's A Gifted Man (9.1m/1.3) and Fringe (3.1m/1.2) on Fox.
At 10pm, Blue Bloods led the way with 11.2m (1.7), also retaining its title as most-watched broadcast in primetime. Current affairs rivals, NBC's Dateline (5m/1.3) and ABC's 20/20 (4.7m/1.3), both achieved respectable audiences.
Elsewhere, Nikita (1.2m/0.4) and Supernatural (1.1m/0.4) on The CW were repeats.
