Washington: Reigning US Open champion Sloane Stephens was ousted by Germany's Andrea Petkovic while Australia's 17th-ranked Nick Kyrgios withdrew because of a hip injury Wednesday at the ATP and WTA Washington Open.
Petkovic, ranked 91st, rallied to beat the world number three 2-6, 6-4, 6-2 in a second-round match in the hardcourt tuneup event for the US Open.
"I played OK, could have played better," Stephens said. "She played a good match. Today just wasn't my day. I didn't serve great. She just played better."
Stephens, this year's French Open runner-up and a Miami Open champion in March, was broken twice in both the second and third sets in falling to 3-2 against Petrovic, losing for the first time since their initial meeting in 2011 when the American was only 18.
"Hopefully some things will connect in the next few weeks coming into the US Open," Stephens said. "Just focus on my game and get in a few more matches."
Japanese third seed Naomi Osaka, ranked 17th, is the only top-45 player remaining in the women's draw, which saw reigning Australian Open champion and world number two Caroline Wozniacki of Denmark withdraw because of a right leg injury.
The departure of fifth seed Kyrgios came a week after he retired from an Atlanta Open quarter-final with a hip injury and raises concern over his fitness ahead of the US Open, which starts August 27.
"Absolutely gutted to have to withdraw from @CitiOpen," Kyrgios tweeted. "I've done all I can to get my hip ready but ran out of time. I want to thank Keely (O'Brien, tournament director) & her team for the support and apologise to the fans. I'll be back!"
Kyrgios reached the third round last month at Wimbledon after semi-final runs at Stuttgart and Queen's. The 23-year-old from Canberra won his fourth career ATP title in January at Brisbane.
Kyrgios was replaced by 105th-ranked lucky loser Jason Kubler, who was eliminated by fellow Australian James Duckworth 1-6, 6-2, 7-6 (7/5).
Defending champion and world number three Alexander Zverev of Germany was set to finish a rain-halted match against Tunisia's Malek Jaziri after taking the first set Tuesday 6-2.
A victory would lift the top seed into his first ATP matchup against his brother Mischa, the 15th seed who advanced 6-2, 7-6 (9/7) over American Tim Smyczek.
Three-time Grand Slam champion Andy Murray, in his first hardcourt event of a comeback after an 11-month layoff following right hip surgery, faces fellow Briton and fourth seed Kyle Murray in a second-round match.