MADRID May 6 (Reuters) - Britain's Laura Robson and Spain's Carla Suarez Navarro conjured up big first-round upset victories at the Madrid Open when they surprised fourth seed Agnieszka Radwanska of Poland and ninth-seeded Australian Samantha Stosur on Monday.
Robson, the world number 41, thumped Radwanska 6-3 6-1 on the clay at the Magic Box arena and 23rd-ranked Suarez Navarro ousted Stosur 7-6 6-2 to delight the home crowd with her seventh career victory over a top-10 player.
Radwanska was the biggest casualty as second seed Maria Sharapova of Russia eased past Romanian qualifier Alexandra Dulgheru 7-5 6-2 and third-seeded Belarussian Victoria Azarenka had to fight past Russian Anastasia Pavlyuchenkova 7-6 7-6.
Suarez Navarro, who has never won a WTA tour title, was playing her first match since losing to Pavlyuchenkova in the final in Oeiras on Sunday.
"We only had a small window to prepare for today's match, but I was really focused," she said on the WTA website.
"Once I got here to Madrid, I didn't think of what happened in Oeiras for a single moment," the 24-year-old added.
"I just wanted to play the best I could here today. We only have one tournament here in Spain so for us it's a really important week."
World number one and top seed Serena Williams continues her Madrid title defence with a second-round match against Spaniard Lourdes Dominguez Lino on Tuesday. (Reporting by Iain Rogers, editing by Ed Osmond)