By Larry Fine NEW YORK (Reuters) - Grand slam king Roger Federer showed off his fitness by sprinting into the round of 16 at the U.S. Open on Saturday, beating Adrian Mannarino 6-3 6-0 6-2 to turn out the lights on Day Six of the tournament. Playing the closing contest of Saturday's night programme, Federer ran through games as though he had a taxi cab waiting outside the stadium with the meter running and hurtled past the unseeded Frenchman in 81 minutes. "I like it like this," said Federer. "I like three hours, five hours, too, as long as I end up winning them. ... Click here to read full news..