American swimmer Michael Phelps, already the most decorated Olympian of all time with 21 medals, seeks medal 22 Saturday in the men's 4 by 100 medley relay at the 2012 Olympic Games in London. The race will be the last of his Olympic career.

U.S. tennis star Serena Williams and Russian Maria Sharapova face off in the women's gold medal match.

Jamaican sprinter Usain Bolt makes his debut on Day 8 of the Olympics in a 100-meter preliminary round. Bolt holds the world record in the event.

A South African sprinter will enter the history books Saturday when he runs a 400-meter heat. Oscar Pistorius – known as the Blade Runner – will be the first double amputee to compete in the Olympics. Born without fibulas – the outer bones in the lower leg – Pistorius wears special prosthetics from just below the knees.