Liem, the second seed, logged one win and one draw to accumulate 4.5 points, enough to set his lead in the tournament.
Theworld No. 65 easily beat Zhang Zhong of Singapore in the fourth roundbefore tying with teammate Nguyen Duc Hoa in the fifth.
The No. 1 seed Li Chao of China also earned the same number of points and could steal Liem's position.
He has beaten veteran chess master Dao Thien Hai of Vietnam and temporary leader Pitra Andika from Indonesia.
Li is scheduled to meet Liem in the sixth round match at the De Nhat Hotel.
Asthe two top candidates vie for the title, their match at board No. 1 isexpected to draw a lot of attention from spectators and experts.
The March 19 rounds saw the return of defending champions Nguyen Ngoc Truong Son.
After a losing streak during the first two days, Son logged two winsin a row, beating veteran rivals Liu Xiangyi of Singapore and LayloDarwin of the Philippines.
The victories helped Son retain the hope of protecting his title as there are still four matches ahead.
He will compete against teammate Hoa in the morning.
Hoa, Zhang Zhong of Singapore and Pascua Harida of the Philippines have four points each and are tied with Son.
All of them are just 0.5 points short of the leading group.
During this year's tournament, organisers will award a bonus to thebest female master. At present, Karavade Eesha of India is leading thechart with 3.5 points after five games.
Vietnamese Le Kieu Thien Kim is close behind with three points.-VNA