(Reuters) - Sloane Stephens began the build-up to her U.S. Open title defence with a 7-5 6-4 win over wildcard Bethanie Mattek-Sands back on the American hardcourts at the Citi Open in Washington, DC on Tuesday.
Stephens, who won her first career title in Washington in 2015, finished off Sands with her sixth ace of the match to book a second round meeting with Germany's Andrea Petkovic, who was a 6-1 6-1 winner over American Jamie Loeb.
It marked the fifth time in six meetings that Stephens has beaten fellow American Sands, all of the five other matches having been played on clay.
The third ranked Stephens is the top remaining seed in the draw after world number two Caroline Wozniacki withdrew earlier on Tuesday with a right leg injury.
(Reporting by Steve Keating in Toronto; Editing by Ken Ferris)