Striker Nguyen Quang Hai surprisingly slotted home from outside the box just four minutes into the game, opening the score for Vietnam.
Saudi Arabia that have five times qualified for World Cup finals quickly bounced back with the pressing tactic, but they could not break Vietnam’s defence line.
The home team had to rely on long shots and high balls, however, their shots on target did not make it difficult for goalkeeper Tan Truong.
After the intervals, coach Park Hang-seo’s men looked confident to resist continued pressure from hosts Saudi Arabia. But Duy Manh’s red card after a hand ball in the box changed the course of the game.
Salem Al Dawsari and Saleh Al Shehri neatly converted their penalties while Yaseer Al Shahran headed home, securing three points for Saudi Arabia.
Losing 1-3 in the first match, Park’s men will fly back to Hanoi to take on Australian side on September 7. Australia earlier trounced China 3-0.
Saudi Arabia will travel to Muscat to face Oman who earlier beat Japan 1-0 in their opening game.