NEW YORK—Alexander Zverev and Belinda Bencic want a trophy in their hands to go with the gold medals they had around their necks. The Tokyo Olympics tennis champions both moved into the quarterfinals of the U.S. Open on Monday, getting a step closer to their first Grand Slam titles. Zverev beat Jannik Sinner 6-4, 6-4, 7-6 (7) for his 15th straight victory. The No. 4 seed from Germany started that run in Japan, carried it through a title in Cincinnati and then kept right on going at the U.S. Open, where he was the runner-up to Dominic Thiem last year. Zverev said his gold medal is with him in New York. The 24-year-old, who has been accused by a former girlfriend of domestic abuse, joked in his on-court interview that he cuddles with the medal when he’s in bed because he doesn’t have a girlfriend. He said keeping the medal …