Massimiliano Allegri's Bianconeri produced a 2-1 triumph at the Juventus Stadium in Turin to draw first blood in the race for the European title.
The Serie A champions hit the lead inside 10 minutes when former Real Madrid striker Alvaro Morata finished from close range at the back post after Carlos Tevez had seen his initial effort parried away by Iker Casillas.
The opening goal had set the crowd alight but parity was restored soon enough when who else but Cristiano Ronaldo found space at the back post to simply head home James Rodriguez's perfectly weighted pass.
Three minutes before the hour-mark and Juventus had restored their lead over the reigning European champions when Dani Carvajal had brought down Tevez in the area.
The Argentine dusted himself off to fire his spot-kick straight down the middle, sending Casillas the wrong way, for his 29th goal in all competitions for the Turin giants.
The victory gives Allegri's side a slight advantage ahead of the return bout at the Santiago Bernabeu next Wednesday night but Carlo Ancelotti will surely have some tricks up his sleeve as he looks to defend his club's Champions League title.
2014/15 UEFA Champions League - semi-final first leg
Juventus Stadium, Turin, Italy - 41,011