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 (8.65 in 18-49, 17.29 million total viewers). That year-ago opener remains the show’s highest-rated telecast on record.

Last March’s fifth-season finale averaged an 8.16 rating in 18-49 and 15.78 million viewers overall.

“The Walking Dead” was the No. 1 program on Sunday night, even topping NBC’s “Sunday Night Football.” Its 7.4 rating in 18-49 also exceeds all broadcast entertainment telecasts since the start of the television season on Sept. 21, beating the premiere of “Empire” (6.7) by 10%.

AMC will release “live plus-3” ratings information on Friday for Sunday’s “Dead” premiere, which could garner larger percentage gains than usual due to its expanded 90-minute running time. In addition to Major League Baseball playoff action, competition for live viewers also included the big-market NFL game on NBC between the San Francisco 49ers and New York Giants.

On social media, “The Walking Dead” was mentioned in nearly 1 million tweets Sunday (956,480), generating 3.6 billion potential impressions via 825,000 unique users. It was also the No. 1 show Sunday on Facebook.

Series creator Robert Kirkman told Variety at New York Comic-Con last week that season six of “The Walking Dead” would be the “most intense” yet. And in his review of the season premiere, Variety critic Brian Lowry said “Walking Dead” appears to be “very much at the top of its game,” calling it a “pretty irresistible feast.”

The show’s return came one week after “Fear the Walking Dead” ended its successful first season on AMC with a 3.4 rating in 18-49 and 6.86 million viewers overall. These numbers rose in L+3 to a 5.15 in the demo and 10.11 million total viewers, capping the highest-rated season for any program in cable history.

Fox International Channels, meanwhile, announced strong international ratings for the season-six premiere, which was up 17% in rating vs. last season across 18 metered markets and delivered five times the channel’s primetime average.

In the U.K., where “Walking Dead” was up against the Lithuania-England soccer match on ITV, Fox was up 11% vs. last year’s premiere and drew more than four times the audience of its nearest rival. In Germany, it drew the largest viewership to Fox ever, resulting in a record 3.7% daily share of the persons 14-59 in pay TV homes. And in Spain, the premiere episode drew the largest audience for Fox to date, commanding a 2.4% share of live viewing for the timeslot.