From TVGuide.com: "CSI (20.8 mil, down 16 percent from its mondo premiere) again trumped Grey's (18.13 mil, -2.3 mil), albeit not in the key demos. The Office (8.49 mil) lost more than a mil, while Supernatural (2.97 mil) fell short of last season's opener by 800,000."
The Hollywood Reporter reports a rating of 3 million, 1.8/5 (Source), as does Variety.com: "[…]"Supernatural" (1.2/3 in 18-49, 3.0 million viewers overall) was overwhelmed at 9, coming in well below last season's premiere." Source.