In season's final grand slam US Open, defending champions Serena Williams and Marin Cilic have entered third round today.In women's event world number one Serena, on course of a calendar slam, eased passed Kiki Bertens from Netherlands 7-6, 6-3. She now faces Bethaine Sands of US in the third round. Other seeded players Agnieszka Radwanska of Poland and Canadian Eugenie Bouchard also entered third round today.In men's section, 9th seed and defending champion Marin Cilic recorded straight set victory over Russian Evgeny Donskoy 6-2, 6-3, 7-5. Two time champion Rafael Nadal and 10th seed Milos Ranoic of Canada were among others to enter third round.In men's doubles section Indo-Romanian pair of Rohan Bopanna and Florin Mergea entered the second round today. They defeated American pair of Austin Krajicek and Nicholas Monroe 6-3, 6-4.