Official numbers
"Thrones delivered 4.4 million viewers for its premiere at 9 p.m. and racked up 6.7 million viewers for the evening after its two repeats were tallied. That’s up 13 percent from its premiere last year."
http://insidetv.ew.com/2013/04/01/game-of-thrones-premiere-ratings-3/
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Even better than I hoped.