Borussia Dortmund lead Real Madrid at half-time in their Champions League encounter at the Bernabeu.
The visitors could have taken the lead in just the ninth minute, when Reus slipped in Marcel Schmelzer to fire at goal.
However, Iker Casillas came to Real's rescue, saving with his legs. The ball then fell to Robert Lewandowski, but the Pole blazed over the bar.
The Spanish number one was then called upon to deny Kevin Grosskreutz, whose curling shot looked destined for the corner of the net.
It took a fantastic effort from Reus to finally beat Casillas, as the German international volleyed home from Lewandowski's lofted through ball.
Real got themselves back on level terms in the 34th minute through Pepe. Mesut Ozil sent a deep cross into the box and the Portuguese defender towered high to head past Roman Weidenfeller.
Jurgen Klopp's men were not to be denied the lead however, and went back ahead through Mario Gotze on the stroke of half-time.
