Carlsbad, California: World No. 6 seed Daniela Hantuchova of Slovakia lost 6-4, 7-5 to Ursula Radwanska of Poland in a first-round match Monday night at the Mercury Insurance Open.
Hantuchova made an unforced error when she sent a forehand long to give the match to Radwanska.
Earlier, US Olympian Varvara Lepchenko cruised to a 6-3, 6-1 win over NCAA champion Nicole Gibbs in another first-round match.
Radwanska got the better of Hantuchova 6-4, 7-5 in the first round of Mercury Insurance Open in Carlsbad.
Hantuchova, who has had an inconsistent season marked by a left foot injury that caused her to miss more than a month of action, dropped the first set when Radwanska registered the only service break in the fifth game.
Radwanska, the younger sister of world No. 2 Anieszka Radwanska, traded service breaks with Hantuchova early in the second set. Radwanska broke serve again for a 5-4 lead before winning the match on her next service game.
Lepchenko hit an array of winners, including numerous drop shots, to easily defeat Gibbs and advance to a second-round match on Wednesday.
"It takes time to adjust," said Lepchenko, who had not played since losing in the third round on the grass at Wimbledon, the site of the Olympic tournament set to begin July 28. "It's not just the surface, but the balls."
Gibbs won NCAA titles in both singles and doubles for Stanford at the end of May, but had few answers for Lepchenko, who is having her best year as a pro.
Lepchenko, born in Uzbekistan, became a naturalized U.S. citizen in 2007. The left-hander grabbed the fourth and final spot on the U.S. women's Olympic team behind Serena and Venus Williams and Christina McHale.
"I think it will be a lot easier going from the hard courts to grass," Lepchenko said.
With the Olympics less than two weeks away, the tournament has one of its weakest fields in years with just one player from the top 10 — No. 10 Marion Bartoli of France.