Rome: The United States completed a relay double at the world championships on Friday when they retained their men`s 4x200 metres freestyle title with a world record time.
The Olympic champions, led by Michael Phelps, shaved 0.01 off their record from Beijing to triumph in six minutes 58.55 seconds and grab another gold after winning the 4x100 freestyle on Sunday.
Russia took the silver medal and Australia won bronze.
Germany`s Paul Biedermann, who took Phelps`s individual 200 freestyle world title on Tuesday, once again frustrated the American and led at the end of the first leg.
While Phelps trailed by over a second, Ricky Berens put the Americans on top in the second leg and David Walters kept them there before Ryan Lochte held off a late surge from the Russians to steer them home.
Completing the relay double gives 24-year-old Phelps his third gold of the meet and his 20th overall in world championships after he also retained his 200 metres butterfly title on Wednesday.
He will seek to defend his 100 butterfly title in Saturday`s final.