Diane Sawyer was all business on a busy first day as anchor of ABC News' flagship evening newscast on Monday, save for a brief salute at the end to Charles Gibson, whose retirement opened the job for her.

"For you, Charlie Gibson, I hope you had a good day and a great night," Sawyer said, a reference to Gibson's usual signoff.

The centerpiece of the opening broadcast was Sawyer's interview with Iranian President Mahmoud Ahmadinejad, conducted over the weekend. Sawyer confronted Ahmadinejad on a supposed "smoking gun" document that tied Iran to development of nuclear weapons. The president, who referred to Sawyer as "respectable lady," said the document was a fabrication.

Women now hold two of the three top jobs on what have always been considered the most prestigious newscasts on broadcast TV. Three years ago, CBS' Katie Couric became the first woman to hold the job by herself.

ABC has deliberately downplayed the transition on "World News." Some of the minor changes promised by ABC executives, including the show's first update of on-air graphics in five years, were evident.

ABC also plans to make use of Sawyer's conversational style, which was on display during on-air Q-and-A's with Jonathan Karl and George Stephanopoulos on health care reform, Lisa Stark on holiday travel and David Muir on holiday gift-giving. Sawyer used a question to Stark at the end of her report to briefly insert news about new rules about how long airlines can keep passengers on idling flights.

The show also featured some plainspoken consumer pieces, including Dan Harris answering reader questions about what the health care reform might mean to them, and Muir discussing what the weekend's major snowstorm in the Northeast might mean for gifts ordered online.

No mention was made that it was Sawyer's first night on the job. Her greeting: "Good evening and it is so good to be here with you tonight."

The show's only real glitch came shortly before a commercial break. Sawyer was previewing a story on actress Brittany Murphy's death and a picture of Ahmadinejad appeared on the screen.

A veteran TV newscaster with a stint on CBS' "60 Minutes" in her background, Sawyer has co-anchored ABC's "Good Morning America" for the past decade. Her 64th birthday is Tuesday.

"World News" is a solid No. 2 in the evening news ratings. NBC's top-rated "Nightly News" with Brian Williams has been consolidating its strength, winning 60 of the past 61 weeks. NBC had its biggest advantage during the November ratings "sweeps" since 2005, according to the Nielsen Co.