The Asian champions from South Korea, the better organised of the two teams, set up a semi-final meeting next week with their South American counterparts Estudiantes of Argentina.
African champions Mazembe of the Democratic Republic of Congo went ahead after 28 minutes in a first half they had the better of against a constant backdrop of brass and drum music from a small but loud group of fans.
Defensive midfielder Mbenza Bedi unleashed a shot from more than 25 metres into the bottom far corner past diving keeper Shin Hwa-yong.
Denilson equalised five minutes into the second half with a close-range header from No Byung-jun's chipped cross from the right to the far post.
The Brazilian struck the winner 12 minutes from time when he beat the offside trap to race through and send his low shot between keeper Muteba Kidiaba's legs.
It quickly became evident a goal would come from Mazembe's defensive frailties at one end or the sheer exuberance of their attacks at the other.
Another factor in the equation was the Steelers' very poor finishing in the first half and the flashy but brave goalkeeping of Kidiaba.
"We have a young side and there were some grotesque mistakes, perhaps due to the nerves of the occasion," Pohang's Brazilian coach Sergio Farias told a news conference.
He said that in the second half "we used the wings more and took off a striker (Namkung Do) to put on a player (Hwang Jin-sung) who could help give the attack more width."
The match was played in unexpectedly fresh weather and the first rain in Abu Dhabi since it fell during a concert by British band Coldplay in April, organisers said.
AFRICAN STRIKE
Mazembe went ahead when an attack crossed the front of the Pohang defence before returning to the middle where Bedi's shot just beat the late dive of keeper Shin who was unsighted.
The Congolese side had survived an early free kick by Kim Jae-sung that took a deflection off the head of a defender and was pushed out at the last gasp by Kidiaba.
The keeper also dived sharply to his left to push away a free kick by No midway through the first half.
Kim Jae-sung, one of four Kims in the starting line-up, shot poorly and straight at Kidiaba with two chances later in the first half when put through on his own as Mazembe failed to catch the Koreans offside.
Mazembe captain Mabi Mputu was just wide with a shot in first half stoppage time that underlined the African champions' willingness to try from distance.
Denilson was denied a hat-trick at the end when Kidiaba saved well at his feet.
