Parviz Mazloumi's side will meet Qatar's Al Rayyan, Al Nasr from the United Arab Emirates and AFC Cup holders Nasaf from Uzbekistan in Group A after goals from Goran Jerkovic, Khosro Heidari and Arash Borhani earned the Tehran side victory.
Esteghlal went into the break 1-0 up thanks to a 38th minute close range effort from French striker Goran Jerkovic, but the game exploded into life on the hour with three goals in six minutes.
Yousef Saleh equalised for the visitors after lobbing the on-rushing Iran national goalkeeper Mehdi Rahmati but two minutes later, Esteghlal regained the lead when Khosro Heidari met Arash Borhani's low, left-wing cross with a shot from 15 yards.
Then, in the 65th minute, Yahya Al Shehri, who was Ettifaq's best player, volleyed wide from a slight angle when he should have equalised.
From the goal kick, Rahmati found Borhani who, cutting in from the left, controlled the ball with his right foot and shot past Hosein Al Subaie to seal the win.
Mazloumi praised his players for an important victory.
"It was a very stressful match and this was a massive win for us," he said. "We needed to reach the ACL or we would have had to play in the AFC Cup and we belong in the ACL.
"We didn't start very well and they were in control in the first 10 minutes but we changed the system and stopped their attacks down the flanks."
He singled out playmaker Mojtaba Jabbari for special praise after his return from injury.
"It was a midfield war and I'm pleased the doctors were able to get Jabbari fit in time as he was excellent," he said
Ettifaq were without their manager, Branko Ivankovic, after the former Iran national boss decided not to travel to Tehran, but his assistant, Andrej Panadic, refused to blame his absence for their defeat.
"Branko's presence would have been important and we were unable to contact him during the match," said the former Yugoslavia international.
"But our defeat wasn't down to his absence. He trusts me and I used his strategies. We lost because we conceded bad and strange goals.
"We could have got back in the game but unfortunately we didn't take our chances. I wish Esteghlal success because they are a big team".