Rome, Italy (My Sportsbook) - Michael Phelps helped the United States' 400- meter medley relay team to a world record in the final event of the 2009 World Swim Championships and earned himself a fifth gold medal in the process.

Phelps swam the butterfly during the third leg of the medley and gave the Americans a big lead, allowing freestyle anchor David Walters to finish the race comfortably in front with a time of three minutes, 27.28 seconds. Aaron Peirsol started the race with the backstroke and Eric Shanteau swam the breaststroke before Phelps did his part in the 43rd world record at the Foro Italico.

The Americans set the old record of 3:29.34 at last year's Beijing Olympics.

Phelps was also part of that relay team in Beijing, when he became the most decorated single-Games Olympian with eight gold medals. He won five this week in a scaled-back program, losing only in the final of the 200-meter freestyle.

In addition to his relay gold on Sunday, Phelps was also part of the winning relay teams in the 400-meter freestyle and 800-meter freestyle. He also captured individual gold in the 100-meter butterfly and the 200-meter butterfly.

American Ryan Lochte captured his second gold medal of the Worlds by winning the men's 400-meter individual medley. Lochte, the 200-meter IM gold medalist, finished in a time of four minutes, 7.01 seconds, beating fellow American Scott Tyler Clary by 3/10ths of a second.

Great Britain's Liam Tancock got the day started with another world record, winning the men's 50-meter backstroke in just 24.04 seconds. He had previously set the mark on Saturday at 24.08 seconds.

Russia's Yuliya Efimova followed with another new record in the women's 50- meter breaststroke, finishing in a time of 30.09 seconds to eclipse the old mark of 30.23 set by Canada's Amanda Reason early last month. Reason finished seventh on Sunday, while American Rebecca Soni was second, just 2/100ths of a second behind Efimova. Another American, Kasey Carlson, was sixth.

Britta Steffen won the women's 50-meter freestyle in world-record time of 23.73 seconds, topping the previous record of 23.96 seconds set by Marleen Veldhuis of the Netherlands this past April. Americans Amanda Weir and Dara Torres were the last two finishers in the field of eight. The 42-year-old Torres, a five-time Olympian, won the silver medal in the 50 free last year at the Beijing Olympics.

Oussama Mellouli of Tunisia captured the men's 1,500-meter freestyle, touching the wall first in a time of 14 minutes, 37.28 seconds. Canada's Ryan Cochrane was second, 4.10 seconds behind.

The women's 400-meter individual medley went to Hungary's Katinka Hosszu in a time of four minutes, 30.31 seconds. World record holder Stephanie Rice of Australia, finished third, while Americans Elizabeth Beisel and Julia Smit were fifth and sixth, respectively.