Wearing shades as he walked back to work following a pizza lunch recently, Brian Williams ducked into Rockefeller Center and passed a tour guide who noted the celebrity sighting to his group: "Ladies and gentlemen, there's Tom Brokaw."

The television business can be humbling, even nearly 10 years after Williams succeeded Brokaw as NBC "Nightly News" anchor. Williams, 55, faces new competition from both ABC and CBS as they look to end NBC's 256-week streak as the most popular evening newscast.

David Muir takes over after Labor Day as anchor of the second-place "World News" at ABC. Steve Capus, former NBC news president and longtime Williams producer, is in charge behind the scenes as Scott Pelley's executive producer at the "CBS Evening News."

"When I started my competition was Dan (Rather) and Peter (Jennings)," Williams said. "That makes me feel old. That gets me on the treadmill every night after work. I am proud of what we've built here."

So far this year, "Nightly News" has averaged 8.9 million viewers and widened its lead over ABC (8 million) and CBS (6.8 million). ABC has gained lately in the 25-to-54-year-old demographic, important to advertisers even as it is a minority of evening news viewers. ABC occasionally wins in that category and, in July, was up 5 percent over last year while NBC was down 4 percent, the Nielsen company said.

"Nightly" is the no-drama newscast at a network where "Today" seeks to regain its mojo against ABC's ratings leader "Good Morning America" and David Gregory is being replaced by Chuck Todd as moderator of "Meet the Press," as the venerable Sunday morning show has fallen from first to third place during Gregory's tenure.

On a summer afternoon, "Nightly" executive producer Patrick Burkey and Williams presided over an afternoon news meeting to go over stories that might squeeze into that evening's 22-minute news hole. Williams takes some ribbing from Todd over the anchor's description of colleague Lester Holt "slappin' the bass" while sitting in with the Roots on the "Tonight" show.

As if to prove a point, Williams repeats the reference on "Nightly."

The biggest change in the job since Williams took over has been the immediacy. Burkey said "Nightly" is much more likely than it once was to change its lineup to reflect late-breaking news and frequently updates the telecast for the West Coast. With social media, if Williams says something mildly controversial or a graphic is misspelled, people at "Nightly" hear about it instantly.

While he's anchoring, TV monitors out of sight of the cameras keep Williams informed of what ABC and CBS are doing on their simultaneous newscasts. Despite this, Williams said it's important to program his broadcast "with blinders on.

"We don't know what the competition is going to do," he said. "While it is true that I am sometimes surprised at the alternatives being offered, it will in no way affect the choices I'm going to make the next day or the day after that."

That's polite anchor-speak. Privately, some at NBC express incredulity over some news decisions made over at ABC — such as a recent day when NBC led its newscast with the shooting death of an American two-star general in Afghanistan while "World News" opened with a collision between double-decker buses in New York's Times Square.

These decisions bear watching, though, since ABC overtook NBC in the morning partly because of a breezier approach that caught NBC flat-footed.

Andrew Tyndall, whose consulting company monitors the content of evening newscasts, said NBC lately seems to be following ABC's lead by introducing more morning-style elements into the second half of "Nightly," including social media pieces by Jenna Wolfe and entertainment coverage.

Williams' spot atop the ratings appears secure, although the change of an anchor lends some mystery to an area of TV where audiences are very loyal.

As Williams finished a second slice of pizza at lunch, he was interrupted by a fellow diner who said she was a fan and thanked Williams for positively representing New Jersey, the state where he has one of his three homes.

"I like that person who just came by," he said after she leaves the hole-in-the-wall pizza joint Williams swears by. "That's really meaningful to me."

Health and ratings permitting, Williams doesn't expect to move onto another job in television news.

"People don't move on from these jobs voluntarily often," he said. "When you're like me, when you came up the way I did, why would you want to do something else?"

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NBC is controlled by Comcast Corp.; ABC is owned by The Walt Disney Co.; CBS is part of CBS Corp.

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David Bauder can be reached at dbauder@ap.org or on Twitter @dbauder. His work can be found at http://bigstory.ap.org/content/david-bauder.