Lopez becomes the first Spanish player to score three times in one match for Barcelona in the history of Europe’s premier club competition.
Lopez struck the opening goal after good work from Lamine Yamal and added a second five minutes before half-time to put Barcelona in control.
Barcelona added more goals after Olympiacos had been reduced to 10 men through Lamine Yamal and Marcus Rashford and Lopez then completed his hat-trick with another fine effort.
The goals make it a great night for Lopez on his first start since returning from injury. He’s likely to start again on Sunday when Barcelona return to action in La Liga with a trip to the Santiago Bernabeu to take on Real Madrid.