Japan and South Korea both suffered deflating defeats in Asian World Cup qualifying matches in the Persian Gulf on Friday.
Striker Vahid Hashemian struck twice to give Iran a deserved 2-1 victory over Japan in front of a raucous crowd of 100,000 in Tehran.
Saudi Arabia beat 2002 World Cup semi-finalists South Korea 2-0 in Dammam thanks to a first-half strike from Saud Khariri and a 65th-minute penalty from Yasser Al Qahtani.
Japan and South Korea, co-hosts of the last World Cup, must recover quickly with all eight teams playing their third games in the final round of Asian 2006 qualifiers on Wednesday.
Bahrain joined Iran at the top of Group B by pinching a 2-1 victory in North Korea in Friday's early game.
Iran and Bahrain have four points from two matches and an identical goal difference following their 0-0 draw in Manama last month.
Japan, who scraped past North Korea 2-1 at home in their opening match, have three points.
Bayern Munich's Hashemian fired Iran in front after 25 minutes at Azadi Stadium with a fierce right-foot shot following a mix-up in the Japan defence.
Midfielder Takashi Fukunishi equalised for Japan midway through the second half but Hashemian headed Iran's winner in the 75th minute after clever play from the industrious Ali Karimi.
"This was the national team's most important victory in recent years," Iran coach Branko Ivankovic said.
"I'm very proud of my team. We removed a very difficult hurdle in our path to the World Cup Finals in Germany."
Saudi Arabia lost 8-0 to Germany in their opening match of the 2002 World Cup but a solid victory over South Korea put them top of Group A with four points from two games.
Khariri swept home from close range in the 29th minute and Al Qahtani secured the points from the penalty spot.
INSIPID DISPLAY
South Korea are bidding to extend their proud record of qualifying for the last five World Cups but a truly insipid display will have concerned Dutch coach Jo Bonfrere.
The Koreans have three points after beating Kuwait 2-0 in Seoul last month.
North Korea were left fuming at the officiating after Thai referee Mongkol Rungklay turned down several penalty claims in a tense match against Bahrain in Pyongyang.
"The refereeing should be fair and today it was not fair -- it was biased," North Korea coach Yun Jong-su said before storming out of a news conference.
Two breakaway goals from Husain Ali left North Korea's dreams of a second World Cup appearance in tatters and were a bitter pill to swallow after the home side had dominated for long periods.
Ali headed Bahrain in front in the eighth minute and the striker volleyed his second after 58 minutes to silence the crowd of 60,000 at Kim Il-sung stadium.
Striker Pak Song-kwan gave North Korea a lifeline five minutes later but Bahrain clung on for victory.
Next Wednesday's visit by Iran is now a must-win game for North Korea, who have achieved little success since their shock quarter-final appearance at the 1966 World Cup.
In Group A, Kuwait earned their first points with a 2-1 home victory over Uzbekistan thanks to two goals from striker Bashar Abdullah.
The top two teams from each group advance automatically to next year's World Cup finals in Germany.
The two third-placed teams face each other for the right to contest a two-legged playoff against a side from the CONCACAF region, with the winners also getting a place in the tournament.
(Additional reporting by Parisa Hafezi in Tehran)
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