Rosberg on top after first day of U.S. practice

By Alan Baldwin AUSTIN, Texas (Reuters) - Formula One championship leader Nico Rosberg and Mercedes team mate and title rival Lewis Hamilton limbered up for their U.S. Grand Prix duel on Friday with each setting the pace in practice sessions. German Rosberg, chasing his 10th win of the season and 33 points clear of the reigning triple world champion, ended the day with the fastest time after lapping the Circuit of the Americas in one minute 37.358 seconds. Hamilton, winner in three of the last f