It’s do or die time for the network television chiefs.

With the new broadcast season entering its third week, the pressure is on top programmers to perform as advertisers who spent some $9 billion on commercial time during the spring ad-sales market decide whether to pass or flunk their fall lineups.

No network chief has more riding on this report card than NBC’s freshman programming chief, Bob Greenblatt, as the network’s new owner -- cable giant Comcast -- is counting on him to restore the fourth-place Peacock to its former ratings glory.

Advertisers spent $1.7 billion on NBC’s fall schedule and, so far, most of his rookie shows, including “The Playboy Club,” “Free Agents” and “Prime Suspect,” have flopped in the ratings. The one exception is the sitcom “Up All Night.”

“NBC is not there, I want to see them do better,” said one major ad buyer. “Thank God for the NFL,” which boosts NBC’s ratings on Sundays.

“Everyone is rooting for them,” the ad buyer said, “but once you‘ve dug a hole” it can be hard to rebound.

NBC has been stuck in last place in the ratings race for six seasons as previous managers emphasized cost-cutting over the popularity of shows, most notably the disastrous “Jay Leno” experiment that pummeled primetime ratings.

For former Showtime executive Greenblatt, it’s not looking good. Greenblatt has said he’s sticking with the current lineup for another week, hoping that commercial ratings that kick in on Oct. 10 and factor in DVR playback give some of his shows a much-needed boost.

At the same time, ad buyers say he may deserve to get a pass for some of NBC’s fall failures because he landed at NBC just as the development season was getting underway.

“There’s much more sampling now with DVRs,” said David Scardino, entertainment specialist with agency RPA. “People used to have to make a choice.”

Amy Sortiridy, senior vice president at ad firm Initiative, said: “There are not a lot of bright spots for them,” before adding, “Greenblatt came in right before development. They may not be his babies.”

Of course, NBC isn’t the only network facing crunch time. ABC is also going through a rough patch, with entertainment chief Paul Lee racking his brain to come up with new hits that can replace aging series such as “Desperate Housewives” and “Grey’s Anatomy.”

One of his darlings, the much-anticipated remake of “Charlie’s Angels,” is proving as hard to bring back as Farrah Fawcett’s iconic feathered hairstyle, with only 7.1 million viewers. Another throwback to the “Mad Men” era, drama “Pan Am,” earned its wings, drawing 11 million viewers in its maiden flight.

CBS and Fox also scored some nice wins. Chris Geraci, head buyer at OMD, said network TV is seeing a sitcom resurgence, thanks to “2 Broke Girls” on CBS and Fox’s “New Girl.”

CBS, the most-watched network, might not be so pleased with “How to Be A Gentleman,” which drew 9 million total viewers but lost 5.5 million of “Big Bang Theory’s” audience.

Fox, which like The Post is part of News Corp., typically has a modest fourth-quarter start. This year, it boasted an additional 31 percent more 18-49 year old viewers -- the most important group for advertisers -- in premiere week versus last season.