Olympiacos also holds the all-time record attendance for a Greek club of 75,263 in a 1982–83 European Cup match against Hamburg at the Athens Olympic Stadium.

Olympiacos has eliminated (in either finals, knockout matches or group stages) clubs like Milan, Arsenal, Ajax, Benfica, Porto, Borussia Dortmund, Lazio, Celtic, PSV Eindhoven, Aston Villa, Werder Bremen, Fiorentina, Anderlecht, Monaco, Deportivo La Coruña, Hertha BSC, Cagliari and Standard Liège among many others.

They have a vast record of home wins over traditional European powerhouses and UEFA Champions League winners like Real Madrid, Milan, Liverpool, Manchester United, Ajax, Juventus, Arsenal, Borussia Dortmund, Benfica, Porto, PSV Eindhoven, Celtic, Aston Villa, Olympique Lyonnais, Olympique Marseille, Atlético Madrid, Valencia, Sevilla, Leverkusen and Red Star Belgrade among many others.

[16] In the third decisive final in Istanbul (a neutral ground), in front of 25,000 fans who filled Mithatpaşa Stadium, Olympiacos beat Levski 1–0 with a goal by Mimis Stefanakos in the 87th minute and won the Balkans Cup.

They managed to eliminate Cagliari in the 1972–73 UEFA Cup, a major force in Italian football during the late 1960s and the early 1970s, (1970 Serie A Champions, 1972 Serie A title contenders), with world-class Italian international players like Gigi Riva, Angelo Domenghini, Enrico Albertosi, Pierluigi Cera, Sergio Gori and Fabrizio Poletti.

[22] The away draw gave Olympiacos the advantage and they finished the job in Piraeus, after a spectacular 2–0 win against the Scottish Champions with Kritikopoulos and Stavropoulos finding the net.

In the second leg in Greece, however, Olympiacos put on a dominant display and almost reached a winning score in a match that was marked by referee Károly Palotai's decisions.

[27] The match is widely known in Greece as the "Palotai massacre"[28][29] with Olympiacos coming close to one of the biggest comebacks in European Cup history.

[18] In the Last 16 they faced Portuguese club Benfica, but despite their comfortable 1–0 in Athens, where Anastopoulos scored the goal and lost a crucial penalty as well, they were eliminated after a 3–0 defeat in Lisbon.

Olympiacos eliminated Monaco and reached the quarter-finals after a hard-fought 1–0 away win in Stade Louis II with a goal by Giorgos Vaitsis in the 86th minute and a goalless draw in Karaiskakis Stadium in the second match.

Their campaign began in the second qualifying round, with Cypriot side Anorthosis not able to prevent them from participating in the group stage for a second time in a row.

They scored the goal that put them in the driving seat in the 12th minute of the game, when Siniša Gogić's powerful header found the back of the net after Grigoris Georgatos's superb cross.

They also missed an outstanding chance to double the lead, when Giorgos Amanatidis' powerful header from short distance was saved by Michelangelo Rampulla.

Eleftheropoulos had been the team's hero in all the previous games, but his mistake condemned Olympiacos, who pushed on in the last 5 minutes to find a goal, but to no avail.

On 11 December, Olympiacos smashed Werder Bremen 3–0 at Karaiskakis Stadium, which ensured their place in the knockout stage of the tournament, where they faced Chelsea.

Olympiacos, after a top-class performance, won the first leg with a convincing 2–0, in a match where they dominated totally and missed chances to even extend the lead.

Despite the two-goal advantage which put them within touching distance of a quarter-final place for the first time since 1999, Olympiacos lost 3–0 in the second leg in Old Trafford, having missed an outstanding double chance to equalize the score in the 40th minute.

Beginning in the Europa League third qualifying round, the club ensured a group stage participation for the third season in a row, after knocking out Belgian KRC Genk and Serbian rookies FK Čukarički.

After knocking out Hungarian champion Ferencváros in the play-offs with 2 Ayoub El Kaabi goals, they faced Israeli Maccabi Tel Aviv in the Round of 16, and got stunned by a 1–4 defeat at Karaiskakis Stadium.

Entering a European quarter-final for the first time since 1998-99, their next opponent were Fenerbahçe, whom they beat 3–2 at home, thanks to goals from Kostas Fortounis, Stevan Jovetić and Chiquinho.

With everything looking like the tie would be settled on penalties, a 116th minute cross by Santiago Hezze landed on El Kaabi's head, who put the ball in Terracciano's net to make it 1–0, causing delirium among millions of Olympiacos fans all over the world.

After a VAR check by Artur Soares Dias, the goal was confirmed and the game ended in that score, with Olympiacos making history and becoming the only Greek football club to win a UEFA competition.