Like most duels, this one starts at dawn.

About 5,000 people, some of them dressed in purple wigs or stars-and-stripes hats, have lined up outside Rumsey Playfield in New York's Central Park in the wee hours of what will turn out to be a beautiful June morning. The attraction? A chance to watch Jennifer Lopez debut songs from her latest album on the nation's most-watched morning show, ABC's "Good Morning America."

Tom Cibrowski, the show's senior executive producer, shows me a helicopter flying high above. The whirlybird is taking shots of this spectacle, which has a difficulty factor, logistically speaking, of 11. George Stephanopoulos, Amy Robach and other members of the "GMA" on-air team have had to tape segments during ad breaks to gain time to be ferried up to the concert site while the show is being broadcast. No matter. Securing J. Lo, says Cibrowski, represents "one of the greatest musical gets of the summer." The show made sure viewers knew that, too, with multiple promos featuring Lopez saying: "I'm live here this morning -- only on 'Good Morning America.' " And it isn't even 9 a.m.

The scene is very similar a few weeks later, when I visit "GMA's" arch-rival, NBC's "Today," which is hosting crooner Jason Mraz in the plaza outside its studios at New York's Rockefeller Center. By 6:30 a.m. on a humid July morning, a line of people hoping to gain access to the show snakes around 48th Street and well up New York's famous Fifth Avenue. Alex Ficquette, an associate producer who joined "Today" in February, will seek people in the crowd who might have an interesting story to tell or have a fervent desire to talk to, say, news anchor Natalie Morales, spotted next to co-host Savannah Guthrie, swaying to Mraz's lilting tunes.

Photo by Craig Cutler for Variety

These glitzy scenes are part of the fiercest competition in television these days, the battle for ayem supremacy between ABC and NBC. Two of TV's most durable programs slug it out daily over a razor-thin margin of victory as they try anything and everything to woo viewers in the lucrative morning news race, where keeping the top spot seems less guaranteed than in years past. There are booking wars, digital innovations and, of late, a flurry of anchor shuffles. With the pace of change on both programs accelerating, the result is a Coke vs. Pepsi-like battle for hearts and minds that won't reach the last drop any time soon.

"Never take for granted being No. 1," says "GMA" co-anchor Robin Roberts. "The sports person in me says that once you do that, you get yourself in trouble. … My mother always said, 'When you strut, you stumble.' "

"Today" led viewership among the coffee-and-cereal crowd for 16 years, but amid the on-air drama of Ann Curry's short tenure as co-anchor opposite Matt Lauer, NBC's cash cow was outmuscled in 2012 by a revived "GMA." The ABC show has maintained that edge, despite the loss of two on-air personalities who helped take it to the top, Sam Champion and Josh Elliott.

Now, reclaiming the morning television crown is nothing short of a mania inside NBCUniversal. CEO Steve Burke made a point of touting "Today's" improved numbers as well as its 18-to-49 rankings during a sit-down session with reporters in March, and the ABC team is just as determined to retain its preeminence.

The competitive fervor between the two shows is heightened by the fact that the difference between No. 1 and No. 2 in the target adults 25-54 demographic is only about 124,000 -- less than two football stadiums' worth of people. Season to date as of July 20, "GMA" has continued to lead "Today" by a handy average of 653,000 viewers overall, according to Nielsen. "GMA" increased its lead in total viewers since September 2013 by 329,000, no small feat when TV viewers are dispersing to all kinds of new video opportunities. "Today" boosted its total audience by 334,000. CBS also has grown total viewership during the past two years, by more than 500,000 for "CBS This Morning" with its newsier makeover featuring anchors Charlie Rose, Gayle King and Norah O'Donnell.

"The viewers aren't just going to come overnight. It's going to take them a while to recognize that it's time to come back," says Don Nash, "Today" executive producer. "We have built it, and now we just need the viewers to come. And they will."

Not, in ABC's view, from those watching "GMA". "We are not going to stop innovating. We are not going to stop trying. We are not going to rest on our laurels," says Cibrowski, describing a mindset more akin to that of a scrappy entrepreneur than an entrenched champion.

On set, the two shows could not be more different. About a dozen crew members work in near silence on "Today," befitting, perhaps, its recent decision to emphasize news coverage after dabbling to ill effect on lurid crime headlines and more frivolous fare. At "GMA," twice as many people -- stylists, carpenters and others -- roam the room, and feel free to speak even while the broadcast is live. Robach, who once anchored the weekend edition of "Today," says she experienced "culture shock" when she arrived at "GMA," where the anchors may laugh at something said off camera or during a commercial break, then talk about it with the audience. "What you see is what you get," Roberts says. "It's not like the camera comes on and we are one way, and then it goes away and we are another way."

The work is grueling. As I discover over four visits to the shows, the human brain does not naturally flicker to life at 4 a.m., which is when the workday starts for most morning-TV folks. Some of the anchors are up even earlier: Stephanopoulos says he rises at 2:30 a.m. each day so he can meditate and take in breaking headlines before he goes on air. When the shows are over, the anchors' day just starts. There are interviews to book, meetings to attend. Before they go to sleep, many of the staffers prep for the next day by reading the latest on breaking stories. Roberts is surprised by people who think her workday ends when "GMA" signs off at 9. Guthrie's advice: Don't slow down. Once you take a break, she tells me, your body wants more rest.

The burden isn't going to get any lighter. "Today" must overcome what NBC News president Deborah Turness calls "a long, slow decline" that actually began in 2000. The show's numbers were so great for so long that producers stopped looking at who might be creeping up on them. By the time "GMA" broke through, the ouster of Curry in 2011 by those in charge of "Today" had an unintended effect. "The action that they took ended up being the very catalyst that propelled (the show) to the No. 2 position almost overnight," she said.