South Korea's Ulsan claimed a slender lead in their Asian Champions League semi-final with a 1-0 win over Harry Kewell's Yokohama F-Marinos in Wednesday's first leg.

The victory also clinched Ulsan's place at next year's Club World Cup.

They qualified as one of Asia's highest-ranking teams and will be one of 32 sides appearing at the expanded competition in the United States.

Lee Dong-gyeong scored in the 19th minute at Ulsan Munsu Football Stadium to give the South Korean champions the advantage heading into next week's second leg in Japan.

The winners will face either Saudi Arabia's Al Hilal or Al-Ain of the United Arab Emirates in next month's two-legged final.

Ulsan are looking to win Asia's top club title for a third time while Yokohama are appearing in the Champions League semi-finals for the first time.

Former Liverpool and Leeds forward Kewell replaced fellow Australian Kevin Muscat as Yokohama coach at the start of the year.

Ulsan made the brighter start and Um Won-sang should have done better when Gustav Ludwigson teed him up in front of goal following a stray pass from the Yokohama defence.

Lee showed him how it was done just over five minutes later, firing Ulsan in front with a crisp left-foot shot from Joo Min-kyu's lay-off.

Ulsan proceeded to sit on their lead and almost paid the price as Yokohama threatened with two free-kicks from dangerous positions late in the first half.

The Japanese side kept up their attacking intent after the break, with Brazilian forward Anderson Lopes giving the Ulsan defence all sorts of problems.

But the Koreans were a constant menace on the counter-attack and Joo hit the post twice in the space of two minutes, the second after a sprawling save from Yokohama goalkeeper William Popp.

Yan Matheus missed Yokohama's best chance to equalise when he missed the target from close range with less than 10 minutes remaining.

Asian Football Confederation teams will fill four places at the Club World Cup.

Al Hilal and Japan's Urawa Red Diamonds have already qualified.