The 10th-seed, who now reached a Grand Slam fourth round for only the second time, raced to a 3-0 lead, with Tien looking sluggish after needing five sets in the previous round to beat Facundo Diaz Acosta.
The American, ranked 18th, went into the match on a six-match winning streak after capturing his first clay title in Geneva last week but by the time he trailed 4-1 in the second set, it was clear his winning run was about to come to an end.
A Cobolli ace and a backhand error from Tien handed his opponent the second set, and Cobolli kept up the pressure to move 3-1 up in the third, courtesy of another early break.
The 24-year-old will next play American Zachary Svajda.