NEW YORK—There is so much to like about the way Madison Keys plays tennis. From her exquisite serve—unquestionably one of the finest motions in contemporary tennis—to her powerful groundstrokes, Keys at her best is as forceful as any player in women’s tennis. Runner-up at the US Open a year ago, tonight the 14th-seeded Keys advanced to the semis for the second-straight time, beating the 23rd seed, Carla Suarez Navarro, 6-4, 6-3, in 83 minutes. But much as Keys can compel, she can also confound.