The last time HBO debuted a new drama series with "Boardwalk Empire," it renewed it two days after the premiere, day the initial ratings came in. HBO has now stuck to that pattern with "Game of Thrones," announcing a second season this morning, not long after final numbers for Sunday night's premiere (which I reviewed here) became available.

The key difference is that, where "Boardwalk" opened with the kind of strong ratings that made renewal a formality, "Thrones" had a good-but-not-great opening audience.

Back in the fall, "Boardwalk" premiered to nearly 5 million viewers in its initial timeslot, and 7.1 million viewers combined for all its airings on opening night. "Thrones," meanwhile, averaged about 2.2 million viewers for its first airing, and a combined 4.2 million viewers for the night. (The HBO press release notably focused on the larger "gross audience" number.)

The early spin I've seen is that "Boardwalk" was promoted all summer during HBO's biggest hit, "True Blood," where "Game of Thrones" was immediately preceded by the low-rated "Mildred Pierce," and before that by the limping final season of "Big Love." And also that "True Blood" started even smaller, with 1.4 million viewers, before growing into the channel's biggest hit, and that perhaps "Thrones" can similarly grow.

Regardless, 2.2 million isn't a bad number for a new HBO series, particularly one in a genre so far outside the channel's comfort zone. And given the huge expense of the first season - an expense that only makes financial sense if HBO can amortize it over multiple years of the show - I imagine any number that wasn't completely disastrous would have led to a second season.

"Game of Thrones" didn't flop, and now Benioff, Weiss and company will get to tell at least two books' worth of stories about it. But I imagine everyone involved would like to see that number rise before a third season starts being seriously discussed.

UPDATE: I was reminded on Twitter that HBO also renewed "Treme" the Tuesday after its premiere, which was modestly-rated. The Tuesday renewal thing seems to be the way HBO wants to do business right now. I am not objecting.

Alan Sepinwall has been reviewing television since the mid-'90s, first for Tony Soprano's hometown paper, The Star-Ledger, and now for HitFix. His new book, "The Revolution Was Televised," about the last 15 years of TV drama, is for sale at Amazon. He can be reached at