CARLSBAD, Calif. (AP) -- No. 6 seed Daniela Hantuchova of Slovakia lost 6-4, 7-5 Ursula Radwanska of Poland in a first-round match Monday night at the Mercury Insurance Open.
Hantuchova lost the match when she made an unforced error, sending a forehand long.
''I'm playing really good the last couple of weeks,'' said Radwanska, who reached the quarterfinals last week at Stanford. ''Now, I know I can beat players from the top 20.''
Earlier, U.S. Olympian Varvara Lepchenko cruised to a 6-3, 6-1 win over NCAA champion Nicole Gibbs in another first-round match.
Hantuchova, who has had an inconsistent season marked by a left foot injury that caused her to miss more than one month, dropped the first set when Radwanska registered the only service break in the fifth game.
''I just went for too many shots, too much to the line,'' said the 32nd-ranked Hantuchova, who was given a wild-card entry into the event. ''She did well to keep the ball in play. I think sometimes I went for too much instead of making her play a little bit more.''
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 and went on to win the match.
''I played very good,'' Radwanska said. ''I was focused the whole match.''
Lepchenko hit an array of winners, including numerous drop shots, to easily defeat Gibbs and advance to a second-round match 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 OIympic 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 top-10 player - No. 10 Marion Bartoli of France.