Vania King (#105) of the US is a former Top 50 player, so it's no surprise that she can reach the third round of a Grand Slam, her second in fact this year, after the French Open. However, since she has concentrated more on doubles, her singles ranking has languished outside the Top 100 for parts of this year.
In the first round, she won over Greta Arn (#63) of Hungary 61 64. Then she made short work of Jarmila Gajdosova (#31) of Australia 26 06. She ran into world #1 Caroline Wozniacki in the third round 26 46 though.
She returns to the Top 100 this week at #94, after her good performance in Flushing Meadows.