Brian Williams’ new primetime newsmagazine Rock Center appears not to be the answer to NBC’s ratings woes. Halloween played a ratings trick on the new show, which opened with a low 1.0/3 in 18-49 and 4.1 million viewers at 10 PM last night. That is below the average for the canceled The Playboy Club that Rock Center replaced (down 38% in the demo from The Playboy Club premiere last month) and lower than the performance of NBC’s veteran newsmagazine Dateline on the less-trafficked Sunday night. It marked NBC’s lowest Monday debut ever. Rock Center‘s lead-in, The Sing-Off (1.4/4), was down 7% from last week to log its lowest rating ever. NBC (1.2/3, 4.3 million) once again finished fifth on Monday among adults 18-49 behind the other major English-language broadcast networks and Univision.