World No 1 Serena Williams crashed out of the WTA Tour’s Family Circle Cup, losing her opening match in straight sets to world number 78 Jana Cepelova.
The 20-year-old Slovakian shocked defending champion Williams 6-4, 6-4 in a second-round match at the clay court tournament in Charleston.
The 17-time Grand Slam winner Williams complained about being mentally fatigued after the 84 minute contest.
“I am really just dead,” said the 32-year-old American. “I need some weeks off where I don’t think about tennis and can kind of regroup. I’ve had a long couple of years.”
Williams, who won this event in 2013, 2012 and 2008, also had her 15-match tour win streak snapped.
Williams was fresh off winning her sixth Miami title and 59th singles crown after beating world No. 2 Li Na, of China, on the weekend.