"We're very happy, these players deserve this", said Real coach Santiago Solari after winning his first piece of silverware since replacing Julen Lopetegui in the dugout in October.
"And I am sure that on Saturday we will do the same or better because it is the real final and we want to finish the year with another prize that would be a third consecutive Club World Cup".
Marcos Llorente hit a stunning 25-yard half-volley - his first professional goal - and Sergio Ramos headed in the third from Modric's corner.
Al Ain's route to the final was more eventful, with wins over Oceania champion Team Wellington in the first stage, Africa champion Esperance of Tunis in the second stage and South American champion River Plate in the final. Benzema - who has six league goals this season - did set up Modric's opener, yet he is ultimately in the Madrid team to score goals, not make them.
Recently-crowned Ballon d'Or victor Modric took one touch before thumping the ball into the bottom corner from outside the box to break the deadlock in the 14th minute.
Al Ain should have taken the lead when Marcelo's mistake let in Hussein El Shahat but captain Ramos made a miraculous goal-line clearance to deny the winger, then Madrid nudged in front.
But the Emiratis hung on and could have levelled when Rayan Yaslam Mohamad Al Jaberi could only slice a shot out of play for a throw-in.
From that point, Real dominated the contest and their home-grown midfielder Llorente doubled the European champions' lead on the hour-mark with a superbly struck volley from outside the area.
Al Ain did pull one back with 5 minutes to go through Tsukasa Shiotani, before putting one through their own net in the first minute of stoppage time.