NEW YORK — Unable to play in the U.S. Open a year ago because of a doping suspension, Marin Cilic is now the tournament's champion. Croatia's Cilic won his first Grand Slam title by beating Japan's Kei Nishikori 6-3, 6-3, 6-3 on Monday at Flushing Meadows, using 17 aces — including four in one game — and the same powerful groundstrokes that helped him eliminate Roger Federer in the semifinals. "This is (from) all the hard work in these last several years — and especially this last year," Cilic said during the on-court ceremony, when he kissed his silver trophy and collected a check for $3 million.