Lee came off the bench to decide a thrilling quarter-final 11 minutes into extra-time and set up another all-South Korean clash on Wednesday.

Ulsan twice came from behind as Han Kyo-won cancelled out Valeri Qazaishvili's 13th-minute opener and Takahiro Kunimoto levelled four minutes into the second half following Yun Il-lok's strike in first-half stoppage time.

Lee stroked his effort beyond goalkeeper Song Bum-kuen from the corner of the penalty area four minutes from the end of the first period of extra-time to keep alive Ulsan's hopes of back-to-back titles.

They will face Pohang who brushed aside Japan's Nagoya Grampus 3-0 in Jeonju.

Lim Sang-hyub scored either side of a strike from Lee Seung-mo as Pohang reached the last four for the first time since winning the title in 2009.

Eight minutes into the second half Lim swept the ball home from close range after the Japanese side failed to clear Sin Jin-ho's corner.

Sin was involved again with 20 minutes remaining when he released Lee to score the second with a drive over Mitch Langerak's head.

There was nothing the Australian goalkeeper could do when Lim curled his second into the top corner deep into stoppage time to confirm Pohang's progress to the last four.

Matches in the knockout rounds of this year's Asian Champions League are being played as one-off games after organisers amended the usual home-and-away format due to travel concerns relating to the ongoing coronavirus pandemic.

Saudi Arabian duo Al Hilal and Al Nassr will meet in the western semi-final on Tuesday after they saw off Persepolis and Al Wahda respectively on Saturday.

The final will be played in Saudi Arabia on November 23 with the winners due to represent the continent at the next edition of the FIFA Club World Cup.

Australian Associated Press