The 2006 winners bounced back from a 2-1 half-time deficit and the loss of their leading striker to end Al-Ittihad's unbeaten home run in the tournament this season ahead of the second leg in South Korea on Wednesday.
Earlier, Al Sadd claimed a precious 2-0 away win over South Korea's Suwon Bluewings in the first leg of their semi-final which was marred by an ugly brawl between the teams which delayed the match for 10 minutes as three players were sent off. .
In Jeddah, K-League leaders Jeonbuk had said they would come and attack the twice winners and they wasted little time in claiming a vital away goal after just two minutes through Brazilian playmaker Eninho.
His low, inswinging right-footed corner found the back of the net via a deflection from Al-Ittihad goalkeeper Mabrouk Zaid to leave the passionate crowd at the Prince Abdullah Al Faisal Stadium stunned.
The home fans were back in full voice shortly after, however, with striker Naif Hazazi rising highest to head a brilliant equaliser from 12 yards in the sixth minute after a cross from Sultan Al-Numare.
The lively Hazazi claimed his second in the 18th minute when Jeonbuk defender Cho Sung-hwan dithered under a high ball and the striker chested down and rifled a left foot drive home from the edge of the area.
Jeonbuk were then dealt a big blow when the tournament's leading goal-scorer Lee Dong-gook was forced off injured in the 34th minute after a heavy challenge from behind by Mishal Al-Saeed.
The tackles were flying in from both sides with Jeonbuk's Son Seung-joon and Al-Ittihad's Osama Al-Harbi booked for reckless challenges as the whistle of Bahrani referee Nawaf Shukralla began to dominate the niggly encounter.
DESERVED EQUALISER
Jeonbuk started the second half brightly and they claimed a deserved equaliser in the 57th minute as they took control of proceedings.
Midfielder Son was allowed time to smash an unstoppable drive into the roof of the net from seven metres after the home side failed to clear a corner.
The impressive Koreans pressed for the winner as the game opened up into an end-to-end attack-fest and Cho redeemed his earlier mistake with a strong header for the winning goal in the 77th minute.
The defender rose to head in an outswinging corner from Eninho although once again Zaid was at fault.
The home side lost their discipline as they grew more and more frustrated and substitute Kim Dong-chan wasted a good chance to increase the margin late on.
