Saudi Arabia took full advantage of an earlier draw between Australia and Japan by beating neighbours United Arab Emirates 3-0 to storm to the top of Group B in Asian World Cup qualifying on Tuesday.
Iran earlier delighted 75,000 fans at a jam-packed Azadi stadium in Tehran when Sardar Azmoun's goal earned a 1-0 win over South Korea that sent Team Melli clear in Group A after four of 10 matches.
The top two in each group reach the 2018 finals with the two third-placed sides meeting over two legs for the chance to face a CONCACAF team in a final playoff for a ticket to Russia.
Saudi Arabia had been expected to be battling it out for third when they were drawn with Australia and Japan but late goals from Fahad Al Muwallad, Nawaf Al Abed and Yahya Al Shehri in Riyadh on Tuesday gave them three wins from four matches.
Bert van Marwijk's side now stand two points clear of Asian champions Australia, who remained undefeated only after rescuing a point from their heavyweight clash with the Blue Samurai in Melbourne courtesy of Mile Jedinak's second half penalty.
Genki Haraguchi put Japan ahead in the fifth minute on the counter-attack but was also responsible for the clumsy challenge on Tomi Juric that allowed the Australia captain to make it 1-1 from the spot in the 52nd minute.
The Saudis top the group with 10 points ahead of the Socceroos (8) and Japan (7) with the United Arab Emirates also still very much in contention on six points.
Mohanad Adbulraheem scored all four goals in Tehran as Iraq secured the first points of their campaign with a 4-0 win over winless Thailand, who were reduced to 10 men after Koravit Namwiset was sent off.
In Tuesday's other qualifier in the Iranian capital, the home side dominated the first half and took a deserved 25th-minute lead through Azmoun, who capped a flowing move when he met a low cross from the right and side-footed it into the net.
The Koreans, bidding for a spot at a ninth straight World Cup, pressed forward after the break but failed to create a clear-cut chance against a packed Iranian defence.
China's fading hopes of qualifying for the finals for a second time received another blow when they were beaten 2-0 by Uzbekistan, who moved up to second in Group A a point behind Iran.
Second half goals from Marat Bikmaev and substitute Shukurov Otabek in Tashkent left the Chinese bottom of the six-team group with a solitary point.
Qatar, hosts of the 2022 World Cup, did finally get their campaign up and running when a first half penalty from captain Hasan Al Haydos gave them a 1-0 win over Syria.
Iran lead Group A on 10 points ahead of Uzbekistan (9) and the Koreans (7) with Syria (4) and Qatar (3) also ahead of China. South Korea host Uzbekistan in the next round of fixtures on Nov. 15.
(Reporting by Nick Mulvenney in Sydney and Simon Jennings in Bengaluru. Additional reporting by Zoran Milosavljevic; Editing by Toby Davis and Pritha Sarkar)