NBC inched ahead of CBS to win Wednesday night with a 1.3/5 rating and 5.53 million viewers, but otherwise it was a primetime of split decisions, declines and plateaus. The night’s top-rated show was Big Brother (2.1/9) and the most-watched show was slot rival America’s Got Talent (1.6/6) with 8.30 million tuning in. Among adults 18-49, the former dipped 5% from last week while the latter bopped up 7% from its August 5 episode – so not a lot of action there. Same meal over on MasterChef (1.4/5), where the Fox show slipped a tenth from last week. Lead-out Home Free (0.8/3) was even with its August 5 airing.

The news was not as good, at least not initially, for an even more recent newbie. In its second week of a three-week double-episode run, NBC’s Mr. Robinson took a tumble and stayed in place at the same time. The 9 PM (1.0/4) episode of the high school music teacher comedy fell 17% from its debut of last week. The 9:30 PM episode (1.0/3) was even with its direct lead-in and with last week’s 9:30 PM episode. That equals among the demo what Undateable did in its second week last year. And NBC is very happy to say the results equal the best any summer comedy has done in its second week since CBS’ Creature Comforts (remember that?) got a 1.4 on June 11, 2007. Not as much to say about Last Comic Standing (1.2/4) last night; while rising 20% from its lead-in, the show fell 20% from last week to hit a season low in preliminary numbers.

Back to one hour after last week’s bigger-than-usual show, Extant (0.7/3) slid 13% into the demo red zone. Over on The CW,  America’s Next Top Model (0.5/2) rose 24% in the demo from last week’s latest premiere ,while freshman A Wicked Offer (0.3/1) was even with its debut.

ABC was all encores Wednesday.