Former champion Jelena Jankovic became the first seed to tumble out of the Indian Wells WTA tournament, losing 6-4, 6-3 to American wild card Jamie Hampton in the second round on Friday.
Seeded 12th, the jet-lagged Serb who had reached the semi-finals in her last two tournaments struggled to find a rhythm as she was broken three times in the opening set and twice in the second.
World No. 1 Victoria Azarenka had to work hard to extend her unbeaten record to 18-0 this year, beating Germany's Mona Barthel 6-4, 6-7, 7-6, while 13th-seeded Russian Anastasia Pavlyuchenkova was ousted 6-4, 6-4 by American Vania King.
Wimbledon champion Petra Kvitova, however, eased into the third round of the elite event with a 6-1, 6-3 demolition of fellow Czech Barbora Zahlavova Strycova at Indian Wells Tennis Garden.
Hampton, who made her debut in the top 100 of the rankings last week, sealed her surprise victory in just under 90 minutes when a Jankovic forehand sailed wide on the stadium court.
"It was a bad day of tennis for me," Jankovic, champion here in 2010, told reporters. "I just did not feel the ball. My legs felt so heavy on the court, so I was moving very badly out there.
"Hampton played solid. She was playing very well. I was really a shadow of myself. I guess it's one of those days where you just come on the court and the legs don't go, the reactions are not there."
Top-seeded Azarenka, who won her first Grand Slam crown at the Australian Open in January, squandered a 5-1 lead in the second set and then came from 1-4 and 3-5 down in the third before sealing a tight victory 8-6 in the tiebreak.
"I won this match mentally more than physically or tactically or whatever," the 22-year-old Belarusian said. "That was really what brought me a win today, my fighting spirit, till the last moment."
In other second round matches, fifth seed Agnieszka Radwanska of Poland brushed aside Romania's Sorana Cirstea while China's eighth seed Li Na battled past Kazakhstan's Galina Voskoboeva 3-6, 6-3, 6-3.
Slovakia's 19th seed Daniela Hantuchova, Indian Wells champion in 2002 and 2007, was beaten 6-3, 6-7, 6-3 by Czech Klara Zakopalova.