Fox’s American Idol continued to keep the pace from premiere week last night, while Bones rose to its best showing in 4 years. But, after a stronger than expected debut last week, NBC’s 3-hour comedy block is starting to show cracks.

Just like it did on Tuesday, American Idol held nicely to its premiere week numbers. Last night, the hourlong show from 8-9 PM drew a 7.6/21 in adults 18-49 and 22.3 million total viewers, down only 3% from last Thursday. Helping things was the fact that Idol‘s biggest competition in the 8 PM hour, CBS’ hit comedy The Big Bang Theory (2.4/7), was a repeat last night vs. an original last week, as was the rest of the CBS lineup except for freshman comedy $#*! My Dad Says (2.3/6), which needs to use up its fresh episodes before it hands off the 8:30 PM slot to Rules of Engagement next month. Against Idol, $#*! dropped 18% in the demo from last week after earlier this month logging matching week-to-week performances behind an original an repeat Big Bang. Also taking a ratings hit in the 8 PM hour was ABC’s reality series Winter Wipeout (2.4/7), down 8% last night, following a 28% drop in its first face-off against Idol last week. Like CBS, ABC aired repeats for the rest of the night.

Fox’s Bones is beginning to settle into its new Thursday 9 PM slot behind Idol. Last night, it drew a 3.9/10 in 18-49, up 11% from last week for a 4-year high. It improved its Idol retention to 51%, up from 46% last week. The next test for the Fox dramedy will come when it faces an all-original competition, especially the similarly skewing Grey’s Anatomy. It goes without saying that Fox (5.8/15, 17.2 million) won last night by a mile.

NBC’s comedy block started off great, with Community (2.2/6) holding steady from last week and tying its best non-Halloween demo result this season. But the rest of the night didn’t go so well. In its second Thursday airing, new comedy Perfect Couples (1.7/4) was down 19%. The drop may have hurt The Office (4.0/11), which was surprisingly down from last week, by 11%, despite featuring the much hyped appearance by the star of the original Office Ricky Gervais. Parks & Recreation (3.0/8) held up relatively well, down 6%, half of the decline of its lead-in. But the 10 PM comedy block is not looking good. Against all-rerun competition vs. an original Mentalist last week, 30 Rock (2.2/6) was down 19% from last week, while Outsourced (1.9/6) climbed a tenth. Things will not be pretty when both The Mentalist and Private Practice return to originals next week. This is not a problem for 30 Rock, which has already been renewed for next season but it is a major one for Outsourced. As the only major network besides Fox to air all-fresh programming last night, NBC (2.5/7, 5.2 million) was No.2 in 18-49, while CBS (2.1/6, 9.6 million) was second in total viewers.

The CW’s Thursday lineup made its return last night, but its fast nationals might be inflated a bit by pre-emptions. The Vampire Diaries (3.5 million, 1.8/5 in 18-34) was up 10% in viewers from its last original broadcast on Dec. 9 and had its best demo delivery since early November. Nikita (2.7 million, 1.0/3 in 18-34) posted its best numbers since October.