China beat Olympic champions Australia with a world record finish to win the women's 4x100m medley relay at the world swimming championships on Saturday. China battled it out with Australia all the way before Li Zhesi touched home in three minutes, 52.19 seconds to shatter the mark of 3:52.69 set by the Australians at the Beijing Olympics. Australia had to settle for silver in 3:52.58, with Germany taking bronze in 3:55.79. American Michael Phelps won a showdown with Serbian Milorad Cavic to claim the men's 100m butterfly gold. Phelps clocked 49.82 seconds to snatch the world record back from Cavic, who shattered the American's mark in Friday's semifinals. Cavic finished 0.13 seconds behind for silver and Spain's Rafael Munoz was third in 50.41. Kirsty Coventry took the women's 200m backstroke in a world record time of 2:04.81. The Zimbabwean beat Russia's Anastasia Zueva by 0.13 seconds. The bronze medal went to American Elizabeth Beisel who clocked 2:06.39. The men's 50m backstroke world record fell in the semifinals when Britain's Liam Tancock touched in 24.08 seconds, shaving 0.25 seconds off the old standard held by Randall Ball. In the women's 800m freestyle final, Denmark's Lotte Friis took gold in 8:15.92 and Briton Joanne Jackson won silver, 0.74 seconds behind. Italian 1,500m champion Alessi Filippi picked up bronze in 8:17.21. Earlier, Brazilian Cesar Cielo Filho added the gold in the 50m freestyle to the 100m gold. In the women's 50m butterfly, Australian Marieke Guehrer claimed gold in 25.48, beating Chinese Zhou Yafei into second by nine hundredth of a second. 