The reigning champions looked set for a shock defeat before Ronaldo stepped up and picked out the top-right corner directly from a set-piece 25 yards out, and Morata secured all three points with a 94th-minute header.
Ronaldo's 350th appearance for Madrid came against the club where he made his debut, and it looked set to be a frustrating one when Bruno Cesar put Sporting ahead two minutes into the second half.
