After years of defying ratings gravity by growing its audience with each season premiere, AMC's "The Walking Dead" finally looked mortal as it kicked off its sixth season Sunday night. According to "live plus same-day" estimates from Nielsen, the zombie drama averaged a monster 7.43 rating in adults 18-49 and 14.6 million viewers overall - up slightly over the show's season 5 averages but below its fall 2014 premiere .