(Flushing Meadows, NY)  --  Third-seeded Serena Williams is into the quarterfinals at the U.S. Open.  The 38-year-old Compton native outlasted 15th-seeded Maria Sakkari of Greece 6-3, 6-7 (8), 6-3 in Monday's fourth round at Flushing Meadows.  Williams is seeking her 24th career Grand Slam singles title, which would tie Margaret Court for the most all-time.