The Iranians, who have already claimed some formidable scalps on their way to the last eight having defeated pre-tournament favourites Bunyodkor and last year's runners-up Al Ittihad, got the winner from a 75th minute penalty, converted by new signing Rajabzadeh after Jung Hong-youn had fouled Igor Castro in the area.
It was the ever-dangerous Castro who had given Zob Ahan the lead after 18 minutes, only to see his Brazilian compatriot Mota equalise 37 minutes later.
The Iranian league leaders enjoyed the best of a bright start to the match with Rajabzadeh heading over a cross from Mohammad Ghazi in the 10th minute.
Eight minutes later a Rajabzadeh corner was headed on by Ghazi to Castro who turned and shot past goalkeeper Shin Hwa-yung.
That woke the visitors up and a period of possession ended with Korea Republic international Seol Ki-hyeon’s header turned around the post by Zob Ahan goalkeeper Shahab Gordan.
After 32 minutes, attacking right-back Mohammad Hosseini, Zob Ahan's leading scorer this season, received a cut-back from Rajabzadeh and crossed for Ghazi, but he failed to hit the target.
Pohang got what could be a crucial away goal 10 minutes into the second half when a right wing cross from Kim Jae-sung was not cleared properly by Farshid Talebi. His header fell to Mota who brought the ball down with his left foot and shot into the bottom corner of the net with his right, silencing the 9,000 fans inside the Foolad Shahr Stadium.
The hosts continued to press, however, as Castro was denied on two occasions by defenders and then shot wide - all in the space of four minutes.
Then, with 20 minutes to go, indecision in front of goal cost Ghasem Hadadifar.
He played a one-two with Ghazi but took too long to shoot from a slight angle and saw the chance disappear with a tackle from Pohang captain Kim Hyung-il.
But Rajabzadeh then scored from the spot with his sixth ACL goal of the season, five of them coming for Mes Kerman in the group stage.
The defending champions could have snatched an injury time equaliser when substitute Hwang Jin-sung saw his shot deflected wide by Gordan in the Zob Ahan goal. The corner eventually fell to Mota on the left edge of the area but his left-foot shot went into the side netting.
Ebrahimzadeh’s Pohang prep pays off
Zob Ahan coach Mansour Ebrahimzadeh cited good preparation as the key to their 2-1 win over Korea Republic's Pohang Steelers in the first leg of their AFC Champions League quarter-final in on Wednesday.
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Goals from Igor Castro and new signing Mahdi Rajabzadeh mean the Iranian league leaders will take a slender lead into the second leg at the home of the defending ACL champions next Wednesday.
Castro's goal, which came after 18 minutes, was particularly pleasing for Ebrahimzadeh, as it resulted from a corner.
"We knew they'd play on the break and we were able to create chances (early on) and we took advantage of their weakness on set pieces to score our first goal,” he said.
The visitors started the better after the interval and equalised in the 55th minute through Castro's Brazilian compatriot, Mota.
"We didn't start well or cover each other as we should in the second half," added Ebrahimzadeh, who is a native of Esfahan.
"But after that (equaliser), our tactics were good and we had excellent chances.”
Ebrahimzadeh was also delighted Zob Ahan performed to the expectations of the Iranian people.
"All Iran was watching us in this match to see what we would do and I'm happy that we were successful,” he added.
Rajabzadeh, who scored five ACL goals for Mes Kerman before signing for Zob Ahan in the summer, dispatched the penalty in the 75th minute to give the Iranians the win.
However, Ebrahimzadeh's counterpart Park Chang-hyun thought it was mistakes from his side that handed victory to the hosts.
"In the second half we made one mistake and gifted them the penalty," said the 44-year-old who is still, officially, the club's caretaker coach.
However, Park believes Pohang will show the sort of form that carried them to success in the tournament last year in next week's return leg.
"We played with a different system, started cautiously and played on the counter attack," he said.
"I accept that we weren't very fast but if you come to Korea next week you'll see a better tempo from us.
"Be sure that in the second leg, especially in the second half, you'll see a superb performance from Pohang.”