By Karolos Grohmann

BERLIN (Reuters) - The United States made amends for their unhappy 4x100m appearances by retaining both men's and women's world titles in the 4x400 meter relays on the final day of the world championships on Sunday.

World and Olympic 400 meter champion LaShawn Merritt teamed up with rival and silver medalist Jeremy Wariner to breeze to victory in the men's 4x400 relay with the year's best time of two minutes 57.86 seconds.

With Angelo Taylor and Kerron Clement also in their formidable line-up, the other teams could only battle for second and third place.

Britain grabbed the silver medal with a determined run by Martyn Rooney, leaving Australia in third.

The U.S. women's team also comfortably defended their relay title with Jamaica in second and Russia third.

Debbie Dunn, running first, handed over to 200m world champion Allyson Felix, having already carved out a 10m lead and by the time anchor Sanya Richards took the baton, victory was all but assured.

Richards helped clock the best time of the year, slashing more than five seconds off the previous season best to come home in 3:17.83.

Both U.S. 4x100 relay teams failed to reach the finals after dropping the baton or handing it over outside the box.

(Editing by Brian.Homewood)