ANALYSIS: With cable steadily gaining on broadcast, a cable show rising to the top of the ratings charts was just a matter of time. But who would’ve predicted just a coupe of years ago that it won’t be a series on established basic cable networks like TNT, TBS, USA Network or FX, which have been nipping at broadcasters’ heels, to do it but a drama on the once-obscure AMC? Yes, the highest-rated non-sports telecast among adults 18-49 on all of television this fall was the Season 3 premiere of AMC’s zombie drama The Walking Dead, which drew 7.3 million 18-49 viewers in Live+Same Day, with no carriage on major satcaster Dish Network no less.

Speaking of fall surprises, who would’ve predicted even a couple of months ago that NBC would leapfrog from fourth to first place this fall to dominate competitors among adults 18-49 by winning each of the first four weeks of the season for the first time in 10 years? That’s since fall 2002, when NBC’s Thursday lineup was anchored by Friends, Will & Grace and ER. NBC has now won seven weeks in a row in 18-49. The rise of NBC to the top of the broadcast standings and cable dramas’ ratings breakthrough highlight the fall season so far.

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Walking Dead proved that the staggering ratings for its season opener were not a fluke, again topping all non-sports competition on broadcast and cable last week with its second airing this past Sunday. Also this month, FX’s biker drama Sons Of Anarchy won the Tuesday 10 PM time slot in 18-49 twice in a row, beating its broadcast rivals, while the cable network’s horror series American Horror Story launched last week as a close second in the Wednesday 10 PM slot among 18-49s to seal cable dramas’ ratings assent. It comes during one of broadcast networks’ strongest periods — the first weeks of the season — when cable networks until recently didn’t even dare to program originals. Also enjoying a successful run against the opening of the broadcast season has been Showtime’s Emmy-winning Homeland, which has broken Showtime ratings records.

What The Walking Dead, Sons Of Anarchy, American Horror Story and Homeland have in common is that they were unlike anything else on TV when they premiered and ended up becoming game-changers for their networks. A similar distinction goes to NBC’s new drama Revolution, which, along with The Voice, has been key to NBC’s ratings turnaround. Revolution (4.3 most current adults 18-49 rating season to date) is the top new broadcast series this fall in 18-49 and the only freshman to crack the Top 10. NBC has the most shows in the Top 10: No.1 Sunday Night Football, the two editions of The Voice and Revolution.

What is remarkable is that NBC has been dominating the season on the strength of three nights — Sunday, Monday and Tuesday — which it has been winning week after week. Those are the nights featuring SNF, The Voice, Revolution and promising new comedy Go On. Meanwhile, the network is barely registering on Wednesday and Thursday. Last week, NBC posted a 1.5 18-49 rating on Wednesday and a 1.4 on Thursday, finishing a distant fourth both nights and getting beat by the CW’s Arrow from 8-9 PM on Wednesday. NBC already cancelled a new series, Wednesday comedy Animal Practice, with freshmen Guys With Kids and Chicago Fire doing only marginally better. But the network accomplished its goal of successfully rebuilding two nights, Monday and Tuesday, to join Sunday. Its weekly victories, which have surprised even NBC brass, came as gravy, courtesy of competitors who are all down from last fall by double digits.

With the exception of the CW with Arrow, no other network can claim a breakout hit this season of the likes of Revolution or last year’s 2 Broke Girls, New Girl and Once Upon A Time. (CBS has come close with its Sherlock Holmes reboot Elementary.) That, coupled with across-the-board year-to-year declines for returning shows, paint an unsettling picture for ABC (down 11% in 18-49), CBS (down 18%) and especially Fox (down 25%). Wall Street is taking notice, with analysts raising concerns over the declines. Here are the Big 4 networks’ standings four weeks into the 2012-13 season in adults 18-49 and total viewers:

Adults 18-49

NBC 3.1 rating Up 19%

CBS 2.7 Down 18%

ABC. 2.4 Down 11%

Fox 2.4 Down 25%

Total Viewers

CBS 11.320 million Down 11%

ABC 8.771 million Down 8%

NBC 8.431 million Up 12%

Fox 6.511 million Down 25%