Two years after Celtic's finest moment in 1967, came Slovan Bratislava's greatest day.
The Slovak giants, then part of the former Czechoslovakia, slayed the great Barcelona at Basel's St Jakob Stadium in 1969 to lift the Cup Winners' Cup, their solitary European honour to date.
Their semi-final opponents that season were the then-Scottish Cup holders Dunfermline Athletic, who themselves had a memorable continental campaign that year as they brushed aside the likes of Olympiacos and West Bromwich Albion to get to the last four.
Despite pushing a Slovan side full of Czech internationals - who would appear at the following year's World Cup in Mexico - the Pars lost out narrowly, going down 2-1 on aggregate.
And the rest is history for Slovakia's Sky Blues; they argue it was the most memorable moment in Czechoslovakian football history.
It is a club that has since struggled in Europe, though there have been recent flickers of life with Europa League and Conference League campaigns, with the most recent in the latter producing knock-out European tournament football.
Like Celtic, Slovan have been the dominant force at home, winning each of the last six Slovakian titles with a 16-point chasm between they and nearest challengers Zilina last season.
They are top of the embryonic Fortuna Liga table this season despite suffering a spectacular 5-0 home thrashing by last term's runners-up before the September international break.
As far as Champions League fixtures go, Celtic may never have had a better chance to win their opening game of the tournament proper for the first time since its 1990s rebrand.
Slovan are strong at home, but this is the first time they have qualified for the Champions League at the 12th time of asking.
They are one of five tournament debutants in the new-look competition, and at a full Celtic Park under the lights, it would be a major blow if the Scottish champions don't win this game and boost their own hopes as well as the flagging Scottish co-efficient.
It was a marathon qualification campaign for Slovan to even reach this point.
Vladimir Weiss' side emerged from four ties, beating the Danish champions Midtjylland in the play-off to finally make the leap onto the big stage.
Weiss - who is hoping to overcome a virus to make the trip to Glasgow - has previous when it comes to shocking Celtic having been in charge of Artmedia Bratislava when they infamously ruined Gordon Strachan's bow at the club in 2005.
Strachan had just replaced Martin O'Neill and despite their second-leg heroics, the 5-0 loss in Slovakia saw them knocked out of Europe altogether.
Weiss' son Vladimir junior had a profitable loan at Rangers in the 2010-11 season, setting up Nikica Jelavic for the winning goal in the League Cup final against Celtic. He will be hoping to get the chance to renew acquaintances in his final campaign before retirement.
The visitors may lack Champions League experience but they don’t lack big-game experience.
Robert Mak and Juraj Kucka are European championship veterans with Slovakia.
The former scored twice against Strachan's Scotland in 2018 World Cup qualifying during a 3-0 win in Trnava, while the latter starred against England in the last 16 of Euro 2024 where the Slovaks came within seconds of knocking the eventual runners-up out of the tournament.
Indeed, striker David Strelec, who started all four in Germany, set up their goal against Gareth Southgate's team and has five in 13 so far this season.
Defender Guram Kashia started every game for the Georgia side that entertained so many at the Euros and has faced Scotland three times in the past while his centre-back partner Kenan Bajric has just forced his way back into the Slovenia national squad.
The man to watch is Armenia international Tigran Barseghyan who has scored eight times in 12 appearances this term. He was involved in 29 goals last term, scoring 15 himself.
Regardless, this is not Atletico Madrid, Bayern Munich or Barcelona that Celtic will be facing and despite domestic heroics, Slovan come to Glasgow as big underdogs.
Watch highlights of every Champions League game from 22:00 on Wednesday on BBC iPlayer and the BBC Sport website and app.
There will also be a Champions League Match of the Day on BBC One on Wednesday, from 22:40 to 00:00.