Day Seven of the London Olympics will be remembered as the final triumph for perhaps the greatest Olympian of all time.

American Michael Phelps won the 18th gold medal of his illustrious career as the U.S. finished first in the 4x100-meter medley relay on Saturday. Phelps decided to retire after the Olympics and the 27-year-old's sensational efforts in England will be remembered for his ability to stay on top of the sports, winning two gold medals and one silver in individual competition, to go along with two golds and one silver in group competition.

The women's swim team was also victorious on Saturday, and set a world record, as well. The U.S. clocked in at 3 minutes, 52.05 seconds, to take the gold. Missy Franklin led things off with the backstroke leg, followed by Rebecca Soni with the breaststroke, then Dana Vollmer with the butterfly, and the anchor went to Allison Schmitt in the freestyle.

In tennis, Serena Williams became only the second woman to complete a career Golden Slam when she won her first singles gold medal  by defeating Maria Sharapova 6-0, 6-1. Williams, who has won 12 grand slams, joins German Steffi Graf, who won 22 grand slams, and a gold in the 1988 Olympics in Seoul.

While Williams has been dominant in the Olympics, so has the U.S. men's basketball team, but the the Americans received a major scare against Lithuania, but still came away with the victory, 99-94. The U.S. needed some late-game heroics from LeBron James to hold off Lithuania, as the Miami Heat star scored nine points in the final four minutes.

Shelly-Ann Fraser-Pryce won the 100-meter dash, clocking in at 10.75 seconds and edging American Carmelita Jeter by .03 seconds.

American Jamie Beyerle Gray won the gold in women's 50-meter three-position while setting two Olympic records -- one in qualification and one in total points.

But the highlight of Saturday may have belonged to Oscar Pistorius. The South African sprinter, who is a double amputee and uses carbon-fiber artificial limbs, advanced to Sunday night's semifinals in the 400-meter heat.