The Williams sisters continued their march towards more Olympic success with three victories between them in London on Monday. Fourth seed Serena romped into the third round of the women's singles with a 6-2 6-3 win over Poland's Ursula Radwanska, whose older sister Agnieszka she beat to win her fifth Wimbledon title earlier this month. The American will next face Russian 13th seed Vera Zvonareva, who knocked out 2010 French Open champion Francesca Schiavone. Zvonareva, the bronze medalist at Beijing four years ago, triumphed 6-3 6-3. It was tough conditions, a little windy. I 'm glad I was able to pull through, said Williams, who faces a possible quarterfinal against former world No. 1 Caroline Wozniacki or Slovakia's Daniela Hantuchova as she seeks the only major title missing from her collection. Her older sibling Venus, who is in the same half of the draw, bounced back from her early exits at the French Open and Wimbledon by thrashing Roland Garros runnerup Sara Errani 6-3 6-1 in her delayed first-round match. Another gold medal would be amazing, said the 32-year-old, who won the singles title in 2000 along with the doubles, which she and Serena won again in 2008. I ca n't even imagine the feeling, I think my head would be too big and no one would even like me anymore. I 've got to get there first, I have two chances and I 'll go for it. Venus will next play Canada's