American tennis stars Venus and Serena Williams, who have collectively won nine Wimbledon singles titles in the past, were both eliminated on Monday during the fourth round of this year's tournament. It marks the first time in five years that neither of them reaches the last eight at the All England Club. And current world number one, Denmark's Caroline Wozniacki, was also sent packing after a tough loss in three sets, failing again in her bid for a first grand slam title. Meanwhile, Maria Sharapova of Russia scored a comfortable win over China's Peng Shuai to advance to her first Wimbledon quarterfinal since 2006. On the men's side, the top four seeds all advanced as expected, but defending champion Rafa Nadal injured his left foot during an intense match against Argentina's Juan Martin Del Potro, casting doubt on the Spaniard's bid for his 11th major title. Nadal is scheduled to meet American player Mardy Fish next, and will likely face British hope Andy Murray in the semi-finals.