More and more viewers are getting swept up by HBO’s “Game of Thrones,” with Sunday’s season premiere setting another series high in the ratings.

Once considered something of a niche show, “Thrones” is now delivering numbers topped on cable only by AMC’s “The Walking Dead.” Nielsen estimates than an average audience of about 8 million watched the initial telecast of “Game of Thrones” on Sunday — up 1.16 million viewers (or 17%) from its year-ago debut of 6.84 million. It’s also about 800,000 more than any other episode of the show to date.

“Game of Thrones” first drew 4 million viewers for an episode with its season 2 finale, then surpassed 5 million viewers for the first time midway through Season 3. It hit the 6-million mark with its season 4 premiere, passed 7 million with its fifth episode last year and now 8 million. Its peak had been the seventh episode of last year, which drew 7.195 million.

And like “The Walking Dead,” “Game of Thrones” has grown its average seasonal audience with each year. The first season of “Thrones” in 2011 averaged 2.52 million viewers for its initial Sunday telecast, according to Nielsen “live plus same-day” estimates. It has grown in successive seasons to 3.8 million in 2012, to 4.97 million in 2013 and then 6.84 million in 2014.

It seems well on its way to extending that streak again this year.

In adults 18-49, primetime’s most important demo but one that has little effect on a premium service like HBO, Sunday’s premiere of “Game of Thrones” averaged a 4.19 rating (or about 5.3 million viewers). This is up 14% from last year’s premiere score (3.61) and is 6% higher than the show’s peak in the seventh week (3.95).

By comparison, AMC’s season finale of “Walking Dead” two weeks ago did an 8.16 rating in Nielsen’s “live plus same-day” averages while averaging nearly twice as many total viewers as “Thrones” (15.8 million).