Duan, of the team VUS-HCM City, finished first in the 175km race from Quang Ngai to Quy Nhon city. He completed the course in 4:31.28 with an average speed of 38.679kmh.
Nguyen Thanh Tam and Huynh Thanh Tung of the Military Zone 7 team were the runners-up. Tung also won the white jersey, given to the best young cyclist.
Duan also won the green jersey as the best sprinter with 177 points, followed by Le Nguyet Minh, also of VUS-HCM City, with 134 points.
Changpad Kritsada of Thailand retained the yellow jersey for the best overall time of 26:04.36 after nine stages, followed by Jiung Jang of the Korail Cycle Team and Ronald Lomomtos of the Philippines NSI.
In the team rankings, the Philippines NSI took the lead with a time of 78:13.22. VUS-HCM City and Korail Cycle Team moved into second and third place, respectively.
Today, cyclists will compete in the 10th stage around the central square of Quy Nhon city, a course of 10km.