After six matches, the Grandmaster has 5.5 points, with five wins and one draw.
In the latest match on October 11in Hanoi time, Liem drew top seed Hikaru Nakamura of the host after 45 moves.
Those following were Nakamura, Wesley So of the Philippines and Yu Yangyi of China.
The Vietnamese will next meet So, who is the defending champion, in the seventh round. So defeated Liem in the fourth round match of the World Cup last month.