Montenegrin striker Dzenan Radoncic opened the scoring in the eighth minute at Tancheon Sports Complex before Yeom Ki-hun equalised nine minutes later.

Mauricio Molina restored Seongnam's lead in the 33rd minute and Radoncic headed home just after the hour to put the hosts in control.

An own goal from Yang Sang-min eight minutes from time ensures Seongnam have a healthy advantage ahead of next week's second leg.

Suwon coach Yoon Sung-hyo blamed the condition of the pitch for his side's hefty defeat.

"I don't really want to talk about the game after playing on that kind of pitch, it was nonsense," he said. "Even Sunday League players would not want to play on that pitch."

Seongnam coach Shin Tae-wong brushed off Yoon's complaints, stressing the problems were the same for both sides.

"I think it is an excuse to keep talking about the grass," he said. "We don't like it either ... but the situation is the same for both teams. We were able to play our football and it wasn't just long-ball."

There was disappointment for one of South Korea's other representatives in the quarter-finals as Jeonbuk Hyundai Motors lost 2-0 to Saudi Arabia's Al Shabab at Jeonju World Cup Stadium.

Fahad Hamad stabbed home from close range in the 68th minute and though Al Shabab were reduced to 10 men in the 88th minute when Abdulmalek Al Khaibri was shown his second yellow card, they added a second goal in stoppage time through substitute Juan Manuel Olivera.

"It is a bad result but we have to accept it," said Jeonbuk coach Choi Kang-hee. "The important thing is that the quarter-finals are not finished yet. If there is only one per cent of possibility to go through we have to keep going on."

Al Shabab coach Jorge Fossati was pleased his side's long trip from Saudi Arabia to South Korea proved profitable.

"I am very happy because we won a very important game," he said. "We travelled a long time and I had to worry about the fitness of my players. Nevertheless we played as we planned and got the result we hoped."

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Defending champions Pohang Steelers lost 2-1 to Iranians Zob Ahan at Foolad Shahr Stadium in Esfahan, although their away goal could prove crucial in next week's return leg.

Igor Castro put the hosts ahead after 18 minutes when he poked home from close range but Pohang equalised 10 minutes into the second half through Mota.

However, Mahdi Rajanzadeh converted a penalty with 15 minutes remaining to give Zob Ahan the slender advantage.

"All Iran was watching us in this match to see what we would do and I'm happy that we were successful," said Zob Ahan coach Mansour Ebrahimzadeh.

Pohang's stand-in coach Park Chang-hyun is confident his side will secure their passage to the semi-finals with victory in South Korea.

"I accept that we weren't very fast but if you come to Korea next week you'll see a better tempo from us," he said.

"Be sure that in the second leg, especially in the second half, you'll see a superb performance from Pohang."

Finally, Al Hilal have one foot in the last four after the Saudi side eased to a 3-0 win over Qatar's Al Gharafa at Prince Faisal bin Fahd Stadium.

Mohammed Al Shalhoub opened the scoring after 13 minutes when he was put clear on goal by Yasser Al Qahtani.

Ahmed Al Fraidi added a second 10 minutes into the second half when he stabbed home the rebound from Thiago Neves' free-kick and substitute Waleed Algizani completed the victory with a fine solo effort in the 85th minute.