Australia's celebrated ex-Socceroo Kewell is seeking to eclipse both of his compatriots Ange Postecoglou and Kevin Muscat, neither of whom managed to land Yokohama the biggest title in Asian club football.

But it will be a tough ask for new boss Kewell too after Lee Dong-gyeong's first-half goal gave Ulsan the advantage going back to Yokohama for the return leg in Japan next Wednesday.

It was a big night for Ulsan, who also booked their place in the inaugural 32-team Club World Cup in the United States next year as one of Asia's four representatives.

Kewell has already broken new ground with the five-time Japanese champions Yokohama, who've never previously reached this stage in the Asia Champions League before, though they did lose what was once the Asian Club Championship final against China's Liaoning in 1990.

There is still plenty of hope for his side with Yokohama, who adopted an aggressive attacking approach after going behind, ending up ruing a missed chance to equalise by Yan Matheus inside the last 10 minutes.

Ulsan, too, will look back on Joo Min-kyu twice hitting the post in the space of two minutes in the second half, with the return now looking fascinatingly poised.

Kewell, who only came on board in December after moving on from Scottish champs Celtic where he had been an assistant to Postecoglou, is still trying to put his own imprint on Yokohama's style, with mixed results so far as they currently lie fifth in the J1 League.

"It's important to understand when I first came into the job it was always going to be a quick turnaround for us because of the AFC Champions League games that were coming up," Kewell, who was a European Champions League winner with Liverpool as a player, had explained on the eve of the match.

"The attitude of the players has been excellent -- the willingness from them to learn a slightly new style. It's been quite easy to implement my ideas, and they've worked very hard in perfecting them throughout the games."

In the other semi-final, featuring western sides from the AFC, Al-Hilal's record-breaking run of 34 consecutive wins was ended later on Wednesday as the Saudi Pro League leaders were beaten 4-2 by UAE hosts Al-Ain, for whom Soufiane Rahimi scored a first-half hat-trick.

Australian Associated Press