Goals to Lee Chun-soo, Lee Sang-ho and Choi Sung-kuk took Ulsan out to a 3-0 lead at halftime on their home ground against an Al Shabab side that went into the match having played only one competitive match this season.
The Koreans, who are half-way through their K-League season, went on with it in the second half with Choi bagging his second, while Brazilians Leandro and Machado also chimed in with goals for the Tigers.
In Jeddah, Saudi Arabia's Al Ittihad, who are aiming for three Asian Champions League titles in a row, took the ascendancy in their tie against Al Karama of Syria with a 2-0 victory at the Prince Abdullah Al Faisal Stadium.
In the crucial period either side of halftime, the defending champions sealed the match with goals from new signings Alhassane Keita in the 43rd minute and Jared Borgetti in the 46th.
Borgetti, who played for Bolton in the English Premier League last season was instrumental in his side's win, setting up the first goal for Keita with a deft through-ball, before hitting the winner early in the second half.
Shenhua see off 9-man Chonbuk
Korea's Chonbuk Motors were reduced to nine men in their 1-0 loss to Shanghai Shenhua, when Kim Hyeung-bum and Raphael Botti were both given straight red cards by Japanese World Cup referee Toru Kamikawa at the Yuan Shen Stadium in Shanghai.
Gao Lin scored a well taken volley in the 32nd minute to give Shenhua the lead, and was then hacked down four minutes later by Kim, who was sent from the field for his indiscretion.
To make matters worse for Chonbuk, second half substitute Botti lasted just 10 minutes before also being red carded for his reckless challenge on Sun Ji in the 76th minute with the return leg in Korea sure to be a spiteful affair.
In the fourth quarter final, home side Al Qadisiya of Kuwait drew 2-2 with UAE's Al Ain after scores were also tied 1-1 at halftime through goals from Al Ain's Nenad Jestrovic in the 23rd minute and Al Qadisiya's Khalaf Salama on the stroke of halftime.
Salama then fired his team into the lead with his second goal just after the break after picking up the scraps from a corner to tap home from close range.
Al Ain would not be denied however, and recent Brazilian acquisition Dodo leveled the scores once more in the 66th minute, also from a corner kick.
The return legs of the quarter finals will be played on Wednesday, September 20 to decide which teams go through to the semi finals of the Asain Champions League.
Ulsan Horang-I (KOR) 6 (Lee Chun-soo 22, Lee Sang-ho 28, Choi Sung-kuk 35, 78, Leandro 69, Machado 87) defeated Al Shabab (KSA) 0
Al Ittihad (KSA) 2 (Keita 43, Borgetti 46) defeated Al Karama (SYR) 0
Shanghai Shenhua (CHN) 1 (Gao Lin 32) defeated Chonbuk Motors (KOR) 0
Al Qadisiya (KUW) 2 (Salama 45, 48) drew with Al Ain (UAE) 2 (Jestrovic 23, Dodo 66)