Real are therefore the first team to win three successive titles in the competition, and have now moved ahead of Barcelona as the team to have won it the most times.
The Croatia midfielder scored the first goal after 14 minutes, taking one touch before thumping the ball into the bottom corner from outside the box to break the deadlock in the 14th minute after Al Ain had missed two early chances to take a shock lead.
Madrid's home-grown midfielder Marcos Llorente doubled the European champions' lead on the hour-mark with a superbly struck volley from outside the area.
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Real captain Sergio Ramos grabbed his side's third goal with a powerful header from a corner before Al Ain, who shocked South American champions River Plate in the semi-finals, got a late consolation goal through Japanese defender Tsukasa Shiotani.
Madrid substitute Vinicius Jr. burst through in stoppage time, firing in a shot which defender Yahia Nader diverted into his own net.
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