WIMBLEDON, England—When Sebastian Korda struck his last competitive shot as a 20-year-old—an overhead winner that closed out a third-round victory over Wimbledon’s No. 22 seed on Friday—the American raised both arms, then doubled over and rested his hands on his knees. Up in a Centre Court guest box, the body language of his father, 1998 Australian Open champion Petr, was strikingly similar. Arms in the air, then leaning forward, reaching for the railing in front of his seat. The younger Korda’s family bloodlines are serving him rather well at the moment. He is the son of two former professional tennis players—he credits his mother, Regina Rajchrtova, with teaching him to be calm on court—and the brother of two current stars in women’s golf—one of whom, Nelly, is ranked No. 1 and just won her first major—and is looking as if he very well could be the men’s tennis star his …