South Korea will now play three-times champions Japan at the Al Gharafa Stadium on Tuesday. Earlier Australia set up a last four meeting with Uzbekistan by beating holders Iraq 1-0, also after extra-time.
"The next match against Japan is one of the most crucial we will play. Japan has been getting better and better throughout the tournament in every aspect of their game but I have never feared the Japanese team," South Korean coach Cho Kwang-rae told reporters.
The Koreans dominated territory and possession for long periods at the Qatar Sports Club but failed to create many clear cut chances as the Iranians defended deeply but effectively, marshalled by the headband-wearing Hadi Aghili.
However, Aghili and his team could not stop Yoon from cutting in off the right flank and angling a left-foot drive into the far corner of the net in the 105th minute to leave Korea dreaming of a first Asian Cup title in 51 years.
"The Iranian team's defensive organisation was very strong they were very compact and very organised I believe not many teams can score many goals against them but we created a couple of chances," Cho said.
NIGGLY START
Cho predicted the Iranians would resort to fouling in the early stages to disrupt his side from playing their short, sharp passing game and he was proved right as heavy challenges flew in from both sides in a niggly start.
Teenage striker Ji Dong-won looked the most likely to break the deadlock for the Koreans with Manchester United midfielder Park Ji-sung also causing problems for the three-times champions.
Ji, 19, went close to opening the scoring on the stroke of half-time but his curling right-foot effort went narrowly wide.
The start of the second half continued in much the same fashion, despite Iran coach Afshin Ghotbi bringing on defender Khosro Heidari to try and stem the flow.
"I could have changed seven or eight players in the first half as they didn't perform to their level," said Ghotbi, who will now step down as coach to take charge of J-League side Shimizu S-Pulse.
With 25 minutes remaining, Iran started to enjoy more possession and ventured out of their defensive shell with captain Javad Nekonam firing a free-kick just over the bar with 12 minutes left.
The start of the 30 minutes of extra-time was littered with stoppages for minor injuries before Yoon, who came on in the 81st minute for Koo Ja-cheol, scored to leave the Koreans dreaming of a third Asian title.
"In the first half we did not play the football we like to play and that had something to do with the quality of the Koreans," Ghotbi said.
"As the game went on we became stronger and started dictating but unfortunately in overtime we took a goal in the wrong moment and it was a fantastic finish."
