Madrid, though, soon started dominating proceedings at the Signal-Iduna Park, and could have taken the lead in the 23rd minute had Angel Di Maria not shot over the Dortmund crossbar from a good position.
Three minutes later Ronaldo failed to keep his attempt on target from the left side of the German champions' penalty box.
However, Dortmund refused to allow Jose Mourinho's side to call all the shots, with Kehl testing Casillas with a brilliant curling effort from 20 yards.
Jurgen Klopp's broke the deadlock much against the run of play in the 36th minute, Lewandowski clinically turning home Kehl's ball from close range after taking advantage of a mistake from Pepe.
However, the German champions' lead lasted just two minutes, as Ronaldo latched on to a precise through ball from Ozil before lifting it over Roman Weidenfeller and into the Dortmund goal.