Radwanska and Bencic both surprised in the first round.
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Agnieszka Radwanska, the top seed, and Belinda Bencic, the youngest player in the top world's top ten, both fell at the first hurdle on a day of shocks and rainstorms at the Aegon Classic.
Radwanska, a former Wimbledon runner-up, had intended to use the grass court event as a springboard for another assault on the oldest Grand Slam title, but was halted 7-5,4-6, 6-3 by CoCo Vandewegh, a hard-hitting American ranked outside the top 30.
Vandewegh had never come close to winning a set against Radwanska's consistently skilful ground strokes in four previous meetings, but used her strength and power to good effect.
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Even after the Pole intelligently played her way back to parity, Vandewegh maintained a fierce flat attack and managed to break serve three times in the final set.
"Last week helped me get out of tricky situations because I had done it before," said Vendewegh, referring to her capture of the den Bosch title on grass last week.
"I don't think I played so bad today - she was just really good," said Radwanska, disappointed to have had little practice on grass because of the bad weather. This was her first tournament on this surface this year.
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Earlier Bencic, arguably the world's most promising player, suffered another injury just ten days after a lengthy spell on the side-lines with a bad back.
The 19-year-old Swiss player's movement had been painful and ponderous before she quit half way through the second set during her first round match against Irina-Camelai Begu.
Bencic's retirement gave the world number 26 from Romania a victory by 6-4, 4-3 retired, though there was hardly a moment when Bencic had been mobile enough to win the match.
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She took a tumble on the damp lush grass in the first game, and as early as the fifth game she was seeking help from the trainer. The injury was later described as a thigh strain. "I continued playing more than I should have," Bencic admitted.
Ends