Diane Sawyer's interview of Rihanna on Friday's "20/20" was a ratings hit and enough to lift ABC to first in the Adults 18-49 demographic for the night. "20/20" averaged 8.2 million total viewers — its biggest audience in over 7 months — and garnered a 2.7 A18-49 rating (9 share). Also, its 2.7 A14-34 rating was the show's best since December 2006.