Real were quickly into their stride, and a superb early run by Vinicius Jr. almost brought the first goal, with his on-target effort needing to be pushed over by Konstantinos Tzolakis.
However, it was Olympiacos who opened the scoring out of nothing. A slick passing move involving Daniel Podence, Ayoub El Kaabi and Chiquinho saw the latter fire a low drive past Andriy Lunin.
A magnificent full-length save from the Ukrainian to deny the goalscorer prevented a seemingly certain second for the hosts as the half progressed, before Kylian Mbappe was left in acres of space to drill home the equaliser.
Two minutes later, the Frenchman then powered home a header from Arda Guler’s cross to stun the hosts and, incredibly, Mbappe completed a seven-minute hat-trick - the second-quickest in UCL history - before the half-hour after beating Olympiacos’ offside trap.
Vinicius then buried a sumptuous effort past Tzolakis, but this time Mbappé had just strayed beyond the last defender in the build-up.
The hosts were all over the place, and Aurelien Tchouameni was next to try his luck, only for his effort to cannon back off the crossbar.
There was still time for Lunin to brilliantly deny El Kaabi before the half-time whistle, though, in a warning for the visitors.
The second half began as the first had ended, with Los Blancos on the front foot. However, just six minutes after the break, Olympiacos substitute Santiago Hezze floated a cross into the box, which was met by an unmarked Mehdi Taremi to reduce the deficit.
Any hopes of a comeback were soon dashed, as Vinicius tiptoed past several defenders before squaring to Mbappe to roll in his fourth of the night.
The remainder of the half saw the visitors toying with their opponents, who only managed sporadic forays up the pitch, but still got on the scoresheet once again when El Kaabi headed past a static Lunin.
Though Olympiacos finished as the stronger of the two teams, it wasn’t enough, and the loss was their first-ever in Greece against the Spanish giants, who ended a run of three games without a win in all competitions.
Flashscore Man of the Match: Kylian Mbappe (Real Madrid)
Click here for more on the match
