NEW YORK >> Diane Sawyer is stepping down as anchor of ABC’s "World News" in September after nearly five years in the job, to be replaced by her regular substitute, David Muir.

The network also said Wednesday that George Stephanopoulos will add the role of chief anchor for live news events to his current jobs as "Good Morning America" co-host and host of the Sunday-morning "This Week" political show.

The exit of Sawyer, 68, is not unexpected. She will remain at ABC News to concentrate on landing big interviews and doing prime-time specials. "World News" was a steady second to Brian Williams at NBC during her tenure, although the ABC broadcast has made gains among younger viewers.

Muir, 40, has been groomed for the job. He steps in when Sawyer is away, and traveled to China to report with her in 2010. He has a high profile on "World News" with his regular "Made in America" series where he does stories across the country.

Muir, from Syracuse, New York, swept floors as a teenager in a local television newsroom. He is a graduate of Ithaca College, just like Bob Iger, head of ABC’s parent Walt Disney Co.

Behind him, ABC is expected to make a strong bid to replace Williams at the top of the evening news ratings, hoping to repeat the success it has had in the morning with "Good Morning America."

As chief anchor of live news events, Stephanopoulos takes over a role traditionally held by the evening news anchor at most network news divisions. Evening news anchor was once considered the top job at a broadcast news division, but ABC does not want to disrupt the team of Stephanopoulos and Robin Roberts that has led the network to the top in the lucrative morning market.

The evening news switch will take place on Sept. 2, said James Goldston, ABC News president.