In modern football, the importance of minor tactical tweaks cannot be overstated and there is a compelling argument that substitutions were the key to Real Madrid's win over PSG on Wednesday night.
Following a breathless first half that eventually ended with the game poised at 1-1, the two sides went out for the second period knowing that the tie could not be won during the ensuing 45 minutes but that it could certainly be lost.
As the game wore on, PSG began to dominate possession, forcing Real into several important blocks and challenges.
That trend continued and as the game moved into its final 20 minutes it was the visitors who looked most likely get an all important winner and return to Paris with the advatange.
Step forward Zinedine Zidane. The Frenchman oped to introduce Marco Asensio and Lucas Vazquez for Isco and Casemiro with just 11 minutes to go, a decision which changed the game.
Real's threat suddenly multiplied significantly, with PSG's right flank - patrolled by Asensio following his introduction - the most regular point of attack.
It didn't take long for this plan to bear fruit as Asensio crossed for Ronaldo to bundle home to give Real the lead just four minutes after his introduction, a trick that he repeated three minutes later as he found Marcelo, with the Brazilian duly sweeping home at the near post to put Real 3-1 up.
Zidane knew that he could overload the left flank late on after PSG counterpart Unai Emery surprisingly opted to replace Edinson Cavani with Thomas Meunier after 65 minutes, leaving the French side with two right-backs on the pitch and no natural attacking outlet down the right-hand side.
For all the criticism of Zidane so far this season, he got his tactics spot on during Wednesday night's game.