Al Ajmi volleyed home Imad Ali's cross after only 20 seconds for what proved the decisive goal at Bangkok's Rajamangala Stadium.

Oman withstood severe pressure from the hosts throughout the 90 minutes but managed to hold on for the win and condemn the Thais to a second successive defeat following their 4-1 opening loss to Japan.

Thailand would have been looking to repeat the 2-0 triumph they posted when the teams met in the Asian Cup finals last year, but were stunned by the Omanis' fast start this time around.

Al Ajmi connected sweetly with his volley from eight yards to beat home goalkeeper Kosin Hathairattanakool following good work by Imad Ali on the right.

The Thais responded well and dominated the remainder of the chances but were unable to find a way past Ali Al Habsi despite a less-than-commanding display from the Oman goalkeeper.

Thailand came close on a number of occasions, thanks in part to Al Habsi looking far from assured when dealing with high crosses into his area.

Teerasil Dangda's header smashed against the crossbar in the 12th minute and Datsakorn Thonglao's late free-kick also grazed the woodwork.

Mohamed Rabia also struck the crossbar with a 25-yard shot for the visitors in a rare foray forward looking to double their lead.

Oman were reduced to 10 men in stoppage time, when midfielder Talal Al Farsi was sent off for a second bookable offence but there was not enough time left for Thailand to capitalise on their numerical advantage.