NEW YORK—Holger Rune lost his maiden Grand Slam match to Novak Djokovic on Tuesday but the brave Dane won over the fickle New York crowd at Arthur Ashe Stadium by refusing to retire despite struggling with painful cramp. Djokovic, a three-times U.S. Open champion and bidding to complete a rare calendar-year Grand Slam on the Flushing Meadows hardcourts, is a popular headliner on the New York stage. But on Tuesday it was the dashing 18-year-old newcomer being showered with cheers for his plucky effort in a 6–1 6–7(5) 6–2 6–1 loss to the world number one. “I never felt anything like this,” said Rune. “It was unbelievable feeling staying there. “I tried to give the crowd something, fight for every point, be pumped and everything. “I mean, the crowd was unbelievable. I couldn’t have asked for more.” The match got underway amid a somewhat flat atmosphere inside Arthur Ashe Stadium …