It wasn't supposed to be this tough for Novak Djokovic in the U.S. Open's third round. He is, after all, the reigning Australian Open champion and firmly entrenched as the No. 3 tennis player in the world. He was, don't forget, the runner-up to Roger Federer at Flushing Meadows last year. Plus, Djokovic's opponent Sunday night, 30th-seeded Marin Cilic, was playing in his first U.S. More...