In the men's draw, Djokovic could face Murray in the quarterfinals.
On the other side of the bracket, Magdalena Rybarikova ousted American Alison Riske in three sets, 7-5, 0-6, 6-4.
The top seed and two-time defending champion defeated Mikhail Kukushkin last night.
World No. 37 scores 6-4, 6-2 win to reach fifth quarterfinal of the season.
Fifth-seeded Spaniard wins final four points of third-set tiebreaker subduing Young, 6-7 (4), 6-3, 7-6 (6).
While the big names were practicing and the big show was prepared, qualifiers got to work.
Rafa's withdrawal from the U.S. Open could have far-reaching implications.
Breaking down the men's draw at Flushing Meadows.
The tennis world wants to know: What's wrong with Nole?