March Madness boosted CBS's audience among the key 18-49 demo Sunday night as an overrun of the Kentucky-North Carolina contest drew 16.66 million viewers in the 7 00-7 30 p.m. half hour. In the Eastern and Central time zones, the overrun pushed each of the night's CBS programs up by about 15 minutes. Nevertheless, CBS trounced its competitors in every half hour as it averaged 12.55 million viewers for the night. ABC placed second with fewer than half that number -- 6.21 million. NBC placed third with 6.05 million, followed by Fox with 4.76 million.