Kiet completed the 50.4km stage in Soc Trang City with a time of 1 hour, 20.02 minutes.
He was followed by Nguyen Hoang Giang of Gao Hat Ngoc Troi-An Giang and Joshua Mari Bonifacio of the Philippines’ team Go for Gold.
The overall ranking remained the same after the fifth stage.
Quach Tien Dung of Military Zone 7 was on top with a total time of 10:48.56.
Nguyen Pham Quoc Khang from Bike Life Dong Nai and Pham Minh Triet of Gao Hat Ngoc Troi-An Giang were second and third, respectively.
Gao Hat Ngoc Troi-An Giang took the lead in the team ranking. Bike Life Dong Nai and Team Go For Gold were close behind.
The sixth stage today will be 30 laps around Hoa Binh Boulevard in Can Tho City totalling 42km.