And on Sunday, a final victory in the 4X100-meter medley relay sealed the deal.

CNN: Phelps wins historic eighth gold medal

Phelps, 27 years old, said Thursday he would retire after swimming the 100-meter butterfly Friday and the medley relay Saturday.

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The first U.S. medal Saturday came when the women's 4x100-meter medley relay team broke the world record en route to easily winning gold.

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She was also part of the winning British 4x100m medley relay squad before claiming the 200m short-course equivalent at the end of the year.

BBC: SPORT | Other Sport... | Swimming | Balfour relishes Jones challenge

In the last day of London's swimming competition, the American women won the 4x100-meter medley relay race, setting a new world record with a time of 3:52.05.

CNN: Phelps nets gold in last race; British hosts bank six

Spitz won seven golds, four individual, at Munich in 1972 and while Phelps could not match that feat, he is likely to take his tally here to eight medals after Saturday's medley relay final without swimming a stroke.

CNN: Phelps wins gold medal number five

But history on Saturday also favored the leaders, as the most decorated Olympian of all time tallied another win with his American teammates in the 4 x 100-meter medley relay, handing Michael Phelps his 18th gold medal in the last race of his storied swimming career.

CNN: Phelps nets gold in last race; British hosts bank six

Phelps had already won the 200 and 400 individual medley and 200 butterfly and 4x200 freestyle relay golds.

CNN: Phelps wins gold medal number five

France's Amaury Leveaux set a new world record in the 50m freestyle with a mark of 20.48, while Italy's men's relay team set a new world best of 1:32.91 in the 4x50m medley.

BBC: Goddard claims gold for Britain