Amanda Knox, left, speaks during an interview with ABC News' Diane Sawyer in New York. (Ida Mae Astute/AP)

If ABC was expecting boffo ratings for Diane Sawyer’s exclusive interview with Amanda Knox, it did not happen.

“Murder. Mystery. Amanda Knox Speaks — A Diane Sawyer Exclusive” attracted an average of 8.5 million viewers at 10 p.m. Tuesday — about 800,000 viewers ahead of CBS’s original “Golden Boy” episode in the same hour.

It was the first TV interview for the Seattle college student convicted of murdering roommate Meredith Kercher in Perugia, Umbria, Italy in 2009; Knox served four years of a 26-year sentence before the conviction was overturned, though her acquittal has since been overturned by the Italian Supreme Court.

Among 18-to-49 year olds who are the bread and butter of primetime TV ad sales, and 25-to-54 year olds who are the currency of news programming ad sales, the interview got edged out by NBC’s “Grimm” in that show’s first outing in the timeslot following singing competition series “The Voice.”

That said, chicks in both age brackets feasted on the juicy Sawyer special about Knox’s sometimes bizarre behavior in the wake of her roommate’s grisly death.

But guys in both demo groups heavily favored NBC’s fairytale crime drama — go figure — drowning out the chicks.

And, ultimately, the Knox interview was one of Sawyer’s lower-rated “gets.”

In November of 2011, 12.4 million tuned in when Sawyer interviewed Rep. Gabrielle Giffords, 11 months after Giffords was shot in the head in an assassination attempt.

And in March of ’12, more than 15 million viewers watched Sawyer interview Jaycee Dugard about her kidnap from a South Lake Tahoe bus stop and 18-year captivity, during which she gave birth to two children conceived by rape.

ABC News announced Wednesday that Sawyer will next conduct the first TV interview with Malala Yousafzai, the 15-year-old school girl from Pakistan, who was shot by the Taliban in October of 2012 because she believed girls should have the right to go to school. Sawyer’s exclusive interview won’t air until October, so as to coincide with the publication of her book “I Am Malala” — in much the same way Sawyer’s interview with Knox was timed to coincide with the drop date on “Waiting to be Heard: A Memoir by Amanda Knox.”