NEW YORK (AP) -- As it did in the morning two years ago, ABC News has broken a long-running winning streak by its rivals at NBC News.
ABC's "World News" beat NBC's "Nightly News" in viewership last week, only a month after David Muir took over as anchor from Diane Sawyer. NBC's Brian Williams-led newscast had ruled for 263 consecutive weeks, a streak that began in September 2009, and for 310 of the past 311 weeks.
Last week ABC's broadcast averaged 8.42 million viewers, while NBC had 8.25 million, the Nielsen company said.
In 2012, ABC's "Good Morning America" broke an even longer winning streak in the morning by NBC's "Today" show. Now ABC consistently wins in the morning, a changing of the guard that has been particularly lucrative for the Disney Co.-owned network.
ABC has been creeping up in the evening ratings the past several months, often winning among the 25-to-54-year-old demographic that advertisers consider valuable, even though most evening news viewers are older than that.
"We're proud of the quality of the broadcast we produce every night and the stories we tell," NBC News spokeswoman Erika Masonhall said. "In an increasingly complex world, 'Nightly News' is the place our audience can turn to for credible, authoritative news they can trust."
ABC News did not comment on the ratings turnover.
NBC suggested its rival's ascension may be short-lived. The network said it was particularly hard hit last week by competition with the baseball playoffs because they impacted markets where "Nightly News" is stronger than "World News." For example, NBC said its ratings were off by 50 percent in Los Angeles on Friday, while the ABC newscast was down by only 4 percent.
NBC said it lost some 200,000 to 300,000 viewers last week in markets where local teams were in the baseball playoffs. ABC's margin of victory last week was 166,000.
People at the ABC and NBC newscasts are in the midst of an intense rivalry, albeit one conducted primarily in whispers. Much of it stems from news consultant Andrew Tyndall, who said in a report last winter that "World News" has become "Disneyfied," or less interested in foreign affairs and politics with a heavier concentration of lifestyle, celebrity or sports stories. The report angered many at ABC.
Tyndall, whose company monitors the content of evening newscasts, said ratings volatility can be expected in the next few months as viewers become accustomed to Muir in the role.
During his first month as anchor, Tyndall said "World News" spent 38 minutes in total discussing the wars in Iraq and Syria, compared to 62 minutes for "Nightly News" and 89 minutes for the "CBS Evening News."
However, Tyndall said there is evidence that NBC has "diluted" its hard news appeal since Muir took over, running several celebrity profiles.
"NBC's celebrity focus in September may be a sign that this middle ground is beginning to feel squeezed and that it has to compete more and more on ABC's turf," Tyndall said. "If so, it runs the risk of incurring more defections from those looking for serious contents, not to Muir, but to the 'CBS Evening News.'"
Masonhall said NBC had no comment on Tyndall's analysis.
Follow David Bauder at twitter.com/dbauder. His work can be found at http://bigstory.ap.org/content/david-bauder.