Hernan Crespo's outfit will take on either Ulsan Hyundai from South Korea or Japan's Yokohama F. Marinos.
Goals from Ruben Neves and Salem Al Dawsari gave Al Hilal victory on the night at the Kingdom Arena.
Leading 4-2 from the first leg at Al Ain last Wednesday, the visitors were rocked inside the opening two minutes as the Saudi Pro League side, watched from the stands by their injured playmaker Neymar, made a blistering start.
The four-times winners reduced the deficit in the fourth minute as a rash challenge in the area saw Kouame Kouadio bring down Brazilian winger Michael and, after a VAR review, Neves smashed his spot-kick into the top corner.
But Al Ain remained resolute, with Kaku heading over the bar before the 2003 champions restored their two-goal aggregate advantage in the 12th minute.
Erik Jorgens cut in from the left and fed the ball to Kaku, who found Yahia Nader on the right and he set up the unmarked Jorgens to stroke the ball past Yassine Bounou from 14 yards having continued his run across the box.
Ahmed Barman then headed against his own crossbar as Al Hilal pushed forward, with Ali Al Bulayhi nodding across the face of the Al Ain goal soon after.
Six minutes into the second half the home side struck again, Al Dawsari slotting his low shot into the bottom corner after Barman's header from Yasser Al-Shahrani's long throw had landed at the Al Hilal winger's feet.
Goalkeeper Khalid Eisa kept Michael's deflected effort out at the near post with five minutes remaining while Sergej Milinkovic-Savic headed over moments later as Al Hilal sought in vain to score the goal that would take the game into extra time.
The result means Al Ain will return to the final for the first time since 2016 when they lost out over two legs to South Korea's Jeonbuk Motors.
Ulsan and Yokohama face off in the second leg of their semi-final in Japan on Wednesday, with the South Koreans holding a slender 1-0 lead.
The first leg of the final will be played in either Japan or South Korea on May 11th with Al Ain hosting the return two weeks later.
