In a major embarrassment for NBC, ABC's "World News Tonight" has beaten NBC "Nightly News" in total viewers during an Olympics week -- for the first time in more than 25 years.

NBC’s loss is unprecedented as the network paid nearly a billion dollars for U.S. broadcast rights to the 2018 Winter Games and typically sees a huge ratings bump for all its programs during the Olympics. This time, however, with NBC's Olympics coverage falling flat for many viewers and big news happening back home, NBC's flagship evening news program lost to ABC.

“That ABC is even challenging during the Olympics has to be a concern for the NBC brass,” Media analyst Jeffrey McCall told Fox News.

Last week, “World News Tonight with David Muir” averaged 9 million viewers, compared to 8.4 million total viewers for “Nightly News.” The last time ABC’s evening newscast beat NBC during the Olympics was back in August 1992 when “World News Tonight” prevailed during the second week of the summer games.

NBC can take some solace in picking up a victory in the key demo, but a ratings analyst who asked to remain anonymous called the total viewer loss “a bit embarrassing” and pointed out that “Nightly News” is trending in the wrong direction.

"That ABC is even challenging during the Olympics has to be a concern for the NBC brass" — Media analyst Jeffrey McCall

“While it's true that ‘Nightly’ remains No. 1 among adults 25-54, they're way down in that category, as well as in total viewers. This while ‘World News’ continues to grow in total viewers and has established itself as the most-watched evening newscast by a healthy margin,” the expert told Fox News.

NBC has sent all of its news stars -- except for Megyn Kelly -- to South Korea to promote the Olympics on NBC's news programs. It's standard practice for NBC which during Olympics games expects its news staff to cover the games as the biggest story in the world. As a result, NBC struggled to cover the tragic school shooting in Parkland, Florida which captured Americans' attention, as well as major developments in the Russia election meddling investigation.

“NBC pays a lot of money for the Olympics and owns that story, but they expect the benefits to be seen across the network. The Olympics coverage provides enough promotional opportunities that ‘Nightly News’ should be able to win the evening news ratings with ease,” McCall said. “Viewers interested in anything non-Olympics could easily be drifting to ABC or even the cable news channels.”

The Hill media columnist Joe Concha said that NBC pays big bucks to air the games and part of the investment is the opportunity to promote other NBC programming to a large audience.

“If NBC Nightly News can't get a bump as it has in the past, that likely is worrisome internally. The problem for NBC is that it is locked into its agreement with the IOC on the Winter Olympics until 2032,” Concha told Fox News. “While the total viewers loss isn't good news, from ad sales perspective, the Peacock still accomplished what it needed to from a revenue perspective [with the demo victory].”

“NBC Nightly News” anchor Lester Holt found himself stuck in Pyonchang for school shooting coverage, while “World News Tonight” anchor David Muir hosted his broadcast from Parkland, as did “CBS Evening News” anchor Jeff Glor.

Not only was Holt in South Korea -- so were many of NBC's top correspondents, leaving the Parkland reporting to back benchers barely recognizable to "Nightly News" viewers.

Daily Caller media reporter Amber Athey said that NBC’s decision to send all of its stars to South Korea “certainly didn’t help” its evening news broadcast in the ratings department, but she also pointed to the network’s polarizing content.

“Olympic viewers like myself were also turned off by the glowing coverage of North Korea and the decision to elevate one figure skater’s feud with Mike Pence,” Athey told Fox News.

Even before the news of NBC's historic loss, NBC insiders were criticizing powerful NBC News Chairman Andy Lack for sending his top talent and producers overseas on a promotional jaunt, while leaving the home front dangerously exposed.

“This is very embarrassing,” an NBC staffer told Fox News last week when it was clear that Lack left NBC News dangerously ill-equipped to cover a breaking event with the importance of the Parkland shooting.

There was also widespread bafflement why Lack did not send the only NBC News star still at home, former Fox News host Megyn Kelly, to Parkland immediately to lead NBC's shooting coverage. Kelly, who makes a reported $23 million a year, remained back in New York, despite having extensive experience covering school shootings.

An NBC staffer who asked to remain anonymous told Fox News that there wasn't much enthusiasm either in Pyonchang or 30 Rockefeller Plaza for sending Kelly to Florida. “Even when she was the only NBC News star left on the continent, the institution didn’t want her down there,” the NBC employee said.

Kelly had already been left out of NBC’s South Korea plans and, according to the New York Post, “threw an Olympic fit” when she learned former “Today” star Katie Couric was summoned out of retirement to host the opening ceremony. NBC did not respond when asked if Kelly had volunteered to travel to Parkland.

Lack, 70, himself had stayed back in New York and not traveled to Pyongchang -- a highly unusual decision as the Olympics are usually a command performance for any high-ranking NBC executive. It's unknown why he didn’t travel abroad and NBC did not respond to request for comment. Lack’s top deputy, embattled NBC News President Noah Oppenheim, made the trip in his absence -- his second trip in recent months to the Korean Peninsula after he led Holt on a disastrous reporting trip to North Korea where he was accused of being duped by regime propagandists.

The humiliating evening news loss -- on the heels of the North Korea debacle -- is the latest in a series of gaffes for Lack and NBC News.

Lack has yet to give a cogent explanation for why they spiked Ronan Farrow's explosive reporting on Harvey Weinstein, which Farrow would take to the prestigious New Yorker magazine to great acclaim. This week, the New York Post reported that Farrow may be "banned" from appearing on NBC and MSNBC to promote a different New Yorker report because Lack was furious with him for repeatedly calling out NBC on the Weinstein affair.

An NBC spokesperson emailed “no” when asked if Farrow was banned from the network.

Meanwhile, Lack has not been transparent about the events that led up to the sudden firing of his close friend, Matt Lauer, for sexual misconduct in November at the height of the #MeToo movement. Parent company Comcast has said its top HR executives are investigating who knew what about Lauer’s behavior during his long reign at NBC. There is no public information about the investigation into its news division, which is apparently still underway three months after Lauer was shown the door.