Karimi's third on 77 minutes finally put paid to some dogged resistance from the 2002 World Cup semifinalists, who had three times come back from a goal down.

South Korea had threatened to pull off the greatest of escapes after Park Jin-Sub's own goal early in the second half, with defender Kim Nam-Il's speculative shot levelling the scores at 3-3 with 20 minutes to go.

But Karimi, whose first-half double had ignited the quarterfinal, managed to get on the end of a free kick from Asian player-of-the-year Mehdi Mahdavikia to settle the encounter.

The result sets up a mouth-watering semifinal between Iran and hosts China, whose coach Arie Haan was among the 31,500 crowd.

The Asian giants, who have won the Asian Cup five times between them, had earlier slugged it out to 2-2 at half-time with the Koreans twice pegging back goals from Karimi.

Karimi put Iran ahead after just 10 minutes, nodding past Korean 'keeper Lee Woon-Jae after Hossein Kaebi hooked across the face of goal.

But South Korea hit back just six minutes later as Seol Ki-Hyeon volleyed home a Park Ji-Sung cross from close range.

Karimi placed another downward header past Lee before tournament top-scorer Lee Dong-Gook tucked away a left-footed volley from a deflected cross on 25 minutes.

Also in the first half, Iranian defender Ebrahim Taghipour was driven out of the stadium in an ambulance following a sickening clash of heads with Korean striker Seol.