Vietnam produced more shots in the opening half, with Le Minh Binh hitting the crossbar from long range. However, the distraction in the defence forced them to concede a goal a few minutes before halftime.
Saudi Arabia capitalised on this advantage to add a second after the break to set up an exciting semi-final clash with Australia.
Vietnam started the match quite well and surprised the Saudi Arabians in the second minute when Tran Danh Trung sent a delightful cross into the path of Le Minh Binh, who just failed to connect with a diving header.
Gong Oh-kyun’s side threatened again in the 11th minute with Nham Manh Dung firing a low drive into the side netting from an acute angle.
Vietnam were denied by the crossbar as Le Minh Binh saw his long-range effort rebound off the woodwork in the 35th minute.
Saudi Arabia then put up pressure and got off the mark in the 41st minute with Al Harbi bursting down the left before firing a low effort past goalkeeper Quan Van Chuan.
After the break, Vietnam intensified their attacks seeking to equalise, but only to see their hope of a comeback dealt a big blow in the 65th minute when Al Harbi provided a cross for Al Brikan to head home from close range to seal a 2-0 victory and a semi-final berth for Saudi Arabia.
The three other semi-finalists include Japan, Uzbekistan and Australia.