NEW YORK—Never fazed, rarely flummoxed, Novak Djokovic is so collected in best-of-five-set matches—even when falling behind, as he has done repeatedly at the U.S. Open.
No opponent, or the prospect of what’s at stake, has been too much to handle. Not yet, anyway. And now he’s two wins away from the first calendar-year Grand Slam in men’s tennis since 1969, along with a men’s-record 21st major championship overall.
