Diane Sawyer’s new gig on ABC World News has given the network a boost in its ratings.

In its first three days on the air last week, ABC World News with Diane Sawyer averaged 8.6 million total viewers, up six percent from the newscast’s season-to-date average under Sawyer’s predecessor Charles Gibson. That’s 500,000 more than the broadcast’s season-to-date average, according to Nielsen. Sawyer began her tenure on Dec. 21 with an exclusive interview with Iranian President Mahmoud Ahmadinejad.

But that boost wasn’t enough to dislodge the top-rated NBC Nightly News from its spot. The Brian Williams-anchored newscast drew 9.37 million viewers last week. CBS Evening News With Katie Couric pulled in 6.16 million.

Sawyer also increased the viewership gap over CBS’ third-ranked Evening News with Katie Couric (6.2 million) to its largest size in 11 months.

NBC’s Nightly News with Brian Williams (9.4 million) remains the broadcast news leader.

Thursday and Friday were excluded from the networks’ tallies because of the Christmas holiday and preemptions.

Now ABC trails broadcast news leader NBC by around 800,000 total viewers and 570,000 25-54 viewers. (A week ago, ABC trailed by 730,000 total viewers and 460,000 25-54 viewers). For the short holiday week, NBC was at 9.37 million total viewers for the week, and 2,840,000 25-54 viewers.

While ABC hasn’t picked up ground on NBC, it has distanced itself from third-place finisher The CBS Evening News with Katie Couric, which averaged 6,160,000 total viewers and 1,830,000 25-54 viewers. (The CBS show slipped a bit week-to-week — 30,000 total viewers and 60,000 25-54 viewers.)

The ABC and CBS programs are now separated by 2.4 million total viewers — a 4% weekly increase. ABC says this is its largest advantage over CBS in 11 months. Compared to the week last year, ABC’s total viewing lead over CBS grew 24% larger.