ORLANDO, Fla. — When shots stopped falling and an 18-point lead nearly slipped away, Tennessee did the one thing it does best: clamp down on defense. Tyreke Key scored 12 points, Jahmai Mashack added 11 and the fourth-seeded Volunteers withstood a late scare to hold off Louisiana-Lafayette 58-55 in the opening round of the NCAA Tournament on Thursday night. Tennessee, …