Backed by the No. 1 show of night in “Once Upon a Time,” ABC was best Sunday in a very tight ratings race. CBS, however, drew the most total viewers. Fantasy drama was tops with a 2.9 rating/8 share in the 18-49 demo, with 9 million viewers tuning in, according to early estimates from Nielsen. Not only was ABC best in the 8 o’clock hour with “Once Upon a Time,” but the Alphabet was tops from 9-10 p.m. as well with “Desperate Housewives” (2.5/6, 8m), which is set to go off the air May 13.