This is the first night of the Live Knockout Rounds, which this season, for the first time, are spread out over three straight nights, Monday through Wednesday. Tonight’s opener is worth watching not only for its intrinsic drama, but for an entertaining subplot. In the taped portions to date, which benefit from heavy editing, new judge Kelly Clarkson has proven herself to be a high-horsepower motor-mouth. On live TV, will she be able to restrain herself?