(Reuters) - Starbucks Corp beat Wall Street estimates for quarterly sales at established cafes on Thursday, as higher prices and customer orders powered a strong growth in the United States, its largest market. Shares of the company rose 2 percent in extended trading. The world's biggest coffee chain said sales at cafes open at least 13 months in its Americas unit rose 4 percent in the second quarter ended March 31, beating the 3.58 percent rise expected by analysts, according to IBES data by..