The win took Son to third place in Group A, which should help him secure a quarter-final berth.
In an earlier game, Son drew with Bu Xiangzhi, one of his main rivals at the Asian Games in China next month.
"It's the first ever time a Vietnamese player has beaten the 12-timeworld champion," said an official from Vietnam Chess Federation, TruongGiang.
"However, the winning move was just a moment ofinspiration for Son, 20, in his battle against the 59-year-old formerworld champion," he said.
He added that any player could lose a game during speed play with just one move.
Six years ago, Son became the second youngest IGM in world chess history at the age of 14 years and nine months.
The 20-year-old started to draw attention in 2000 when he won the World U-10s Chess Championship in Spain .
Meanwhile, Son's teammate, Le Quang Liem overcame the host country'sGharamian Tigran in his fourth game before drawing with Ukraine 'sVasily Ivanchuk. Liem scored 5.5 points that puts him second inGroup A. The event has drawn 16 participants divided into two groups.The top four from each will qualify for the quarter-finals. Thetournament will finish on Oct. 30./.