Carlos Alcaraz launched the defence of his US Open crown with a brisk victory after his opponent suffered an injury on Tuesday as third seed Daniil Medvedev strolled into the second round with a quick-fire win. Alcaraz, returning to the same Arthur Ashe Stadium court where he lifted his first Grand Slam as a teenager a year ago, was always in control after Germany’s Dominik Koepfer rolled his left ankle badly in the opening game. Koepfer tried to continue despite being in obvious discomfort, but finally called it quits while trailing 3-2 in the second set after dropping the first…