Manassero, a 17-year-old from Italy, is one stroke ahead of Mikko Ilonen and Graeme Storm. Six more golfers, including Edoardo Molinari, who won the European Tour's stop in Scotland last week, are tied for fourth at 5-under 66.
Manassero opened his round on the back nine and birdied No. 10. He also had a birdie at the 15th hole. He began his second ninth with birdies on two of their three holes and closed in a flourish with three birdies in the last four holes, including the par-5, 629-yard ninth hole.
"It was a perfect round of golf and a great start to a tournament that is very important to me," Manassero said.
Manassero, who last year became the youngest ever winner of the British Amateur, finished 13th at the British Open and 36th at the Masters in 2010. If he finishes in the first five at Crans Montana, he'll be able to bypass tour qualifying school in November.