Sloane Stephens, coming off a quarter-final run at Wimbledon, crashed out Monday in the first round of the WTA and ATP Washington Open.
The 20-year-old American, ranked 15th in the world and seeded second on the women's side of the $1.76 million hardcourt event, was ousted 7-5, 6-3 by Russia's Olga Puchkova.
"There were some (shots) I really couldn't believe went that far out," Stephens said. "The ball was flying everywhere.
"I just couldn't find it. When you don't practice well it shows. I had a couple rough days, and it showed."
Stephens is already trying to tamp down US Open expectations after beating current world number one Serena Williams on her way to the Australian Open semi-finals, where she lost to then-number one Victoria Azarenka.
"If I lose in the first round, don't be upset," she said. "It's going to be my first time there playing under so much pressure and everyone expecting me to do so well.
"Whatever people say or however they think I should do, they don't practice with me. I just have to go out and do the best I can."
Stephens, who took a post-Wimbledon family vacation to Hawaii, also reached the fourth round at the French Open and the last eight at Wimbledon, losing to eventual winner Marion Bartoli.
"I don't know why I play so well at the Slams and not so well at the rest," Stephens said. "I can fix these things myself and get ready for next week."
Mardy Fish, who has missed most of the past year with heart problems, won his first ATP match since March, rallying to outlast Australian qualifier Matthew Ebden 2-6, 6-1, 6-3.
"I still feel a little uneasy and that's to be expected. It's not all going to be roses right away," Fish said. "These will be the sort of situations I have to get through to be 100 percent. These sort of post-traumatic experiences are what I have to get over.
"A lot of it is mental. A little bit is physical."
Fish faces French 12th seed Julien Benneteau in the second round.
Aussie qualifier Samuel Groth blasted 20 aces to beat American Denis Kudla 7-6 (7/2), 6-2 to book a second-round match against big-serving Canadian Milos Raonic while Aussie Marinko Matosevic ousted another struggling US veteran, James Blake, by 6-2, 7-6 (8/6).
"The first set, I really served poorly, and he took advantage," Blake said. "The second set, I fought back and had a chance. I didn't make my shots when I needed to."
On the women's side, defending champion Magdalena Rybarikova rallied to beat American Christina McHale 2-6, 6-4, 6-2. The Slovakian seventh seed will face compatriot Jana Cepelova in the second round with a possible third-round date against German top seed Angelique Kerber.
"Everyone is looking to beat you, and the pressure is also there," Kerber said. "I just have to try to improve my tennis, and I want to play well this week."