AMC’s Mad Men returned last night for its sixth season with 3.4 million viewers. The two-hour premiere of the period drama was down from the 3.5 million viewers who watched the Season 5 debut on March 25 last year. That premiere was the AMC show’s highest-rated episode ever with last night’s show coming in as the second highest-rated. Head to head with the second week of Season 3 of HBO’s Game Of Thrones for its first hour, the Season 6 debut of Mad Men last night got 1.4 million viewers among Adults 18-49 and 1.7 million viewers among its core demo of Adults 25-54. In terms of that demo, Sunday’s Mad Men was even with the Season 5 debut. Last night’s premiere was up from the 2.7 million viewers who watched Mad Men’s Season 5 finale on June 10 last year. Season 5 of the Matthew Weiner-created series was Mad Men’s most-watched so far with an average of 2.6 million viewers. That was up 15% over Season 4’s viewership average, and up 17% in adults 18-49.