GAEL MONFILS battled hard in the New York heat to edge seventh seed Grigor Dimitrov in three tight sets and reach the last eight.

The Frenchman, seeded 20th, won through 7-5, 7-6 (8-6), 7-5 against the Bulgarian.

Elsewhere, Serena Williams took a medical timeout to have her right ankle re-taped and later double-faulted on the last two points as she and sister Venus lost 7-6 (7-5), 6-4 to Russian duo Ekaterina Makarova and Elena Vesnina in the doubles quarter-finals.