China's bid to qualify for the 2018 World Cup suffered a crushing blow on Tuesday while Iran sprang a shock to establish themselves as the frontrunners in Group A at the expense of South Korea.

The Chinese were outclassed 2-0 by Uzbekistan in Tashkent with the Central Asians scoring twice in the second half through Marat Bikmaev and Otabek Shukurov to leave China bottom of the pile on just one point and almost certainly facing more World Cup heartbreak.

The Uzbeks temporarily topped the group with nine points from four matches but were pushed down to second place later on the day when Iran pulled off a 1-0 win over World Cup regulars South Korea in Tehran to take their tally to 10.

The Chinese, who have invested heavily in football and are eyeing a bid for the 2030 World Cup, have only qualified for the tournament proper in 2002 and needed to raise their game sharply in Tashkent to revive their flagging chances.

Uzbekistan, who have never qualified for the World Cup, opened their account through Bikmaev in the 50th minute, the Lokomotiv Tashkent forward blasting the ball home after playmaker Eldor Shomurodov split open the Chinese defence with a brilliant pass.

The hosts were dictating the game and came close to scoring again moments later, but Igor Sergeev's shot crashed back off the post.

But with five minutes remaining Uzbekistan wrapped up a deserved three points after substitute Shukurov's speculative effort took a lucky deflection off Zhang Chengdong and rolled into the net.

An hour or so later, Iran pulled off a surprise win in unusual circumstances in Tehran over South Korea to jump to the top of the group.

Iranian fans faced a tricky balancing act because the game came on a religious holiday in which they are banned from expressing joy.

The game, broadcast live on state television, showed a solemn black stadium packed with subdued spectators wearing black.

Back on the pitch, Iran’s defensive-minded approach in the qualifiers has worked and they have now not conceded a goal in four matches at this group stage.

Sardar Azmoun's goal in the first half was the difference and the frustrated Koreans couldn’t even manage a decent shot at goal.

They take on Uzbekistan next month needing a victory to reignite their 2018 hopes.

Qatar pipped Syria 1-0 for their first win, lifting them off the bottom of Group A.

Hasan al-Haydos struck from the penalty spot in the 37th minute after he was brought down in the box, as the ambitious 2022 World Cup hosts revived their slim chances of making it to a first World Cup finals.

Saudis sneak ahead

Earlier, in Melbourne, Australia came from behind through a Mile Jedinak penalty to grab a 1-1 draw against Japan to remain unbeaten in Group B.

The vistiors rocked the Socceroos with a fifth-minute goal from midfielder Genki Haraguchi but skipper Jedinak retrieved a point in a tense game with his spot-kick.

"We regrouped at half time and we were told to have a reaction. There looked like only one team winning the game, it was unfortunate we didn't get that second goal," said Jedinak.

The stalemate between two of the region's heavyweights put Saudi Arabia in pole position with 10 points in the group after they thrashed neighbours UAE 3-0 in Jeddah.

The UAE kept the Saudis at bay for the best part of an hour but the floodgates opened when Fahad al-Muwallad broke the deadlock in the 73rd minute.

Nawaf al-Abid then added a goal in the 79th minute before the hosts wrapped up their third win in four matches with a strike from Yehya al-Shehri in injury time.

Also in Group B, Iraq notched their first win, a handsome 4-0 over Thailand, with Mohannad Abdulraheem stealing the show by scoring all four goals.