CELTIC'S 2-1 win over Barcelona two weeks ago was described as the second greatest occasion for the club and by a quirk of the fixture list they go back tomorrow to the city where the greatest took place - Lisbon.
It was in the Portuguese capital, on May 25, 1967, that Celtic became the first British club to win the European Cup when they beat Inter Milan 2-1 at the National Stadium.
That team, of which every player was born within 30 miles of Glasgow are now immortalised as the "Lisbon Lions" and if today's side, comprising diverse nationalities, can conjure a victory there and beat Benfica in their penultimate Group G match they will secure their place in the last 16 of the Champions League.
Celtic travel in buoyant mood after the win over Barcelona, the shock of the season so far, lifted them on to seven points in Group G, two behind the Spaniards and three ahead of Benfica. Spartak Moscow are bottom with three.
They returned to the top of the Scottish Premier League with a 2-0 win at Aberdeen on Saturday, their first league win in four outings with both goals coming in a four-minute burst in the second half from substitute Lassad Nouioui and Charlie Mulgrew.
Joe Ledley and Miku, both of whom played against Barcelona, were rested and should be fresh to face Benfica.
Striker Giorgios Samaras was substituted in the 80th minute, while 18-year-old Tony Watt, who came on to score the decider against Barca, played the full 90 minutes but is likely to start on the bench.
Celtic did not play all that well to beat Aberdeen, and will need to show greater resolve against Benfica, who were European champions in 1961 and 1962.
To keep their hopes alive of any further involvement this season, Benfica badly need to win tomorrow as they face a daunting trip to Barcelona in their final group game.
"We need to win against Celtic and, then, we will have a word to say in Barcelona's Camp Nou, said Benfica coach Jorge Jesus.
"It is hard to qualify, but it is not clear that Celtic will win the last match against Spartak Moscow," he added.
"We depend only on ourselves and the maths are done in the end."
Jesus has been hard at work to patch up the Lisbon club's midfield in the aftermath of the high-profile departures of Axel Witsel to Zenit and Javi Garcia to Manchester City.
Although Benfica are yet to convince in Europe, with only a win to their name against Spartak in the last round, they have thrived at home and share the lead of the Portuguese Premier League with Porto.
"We are in a very good phase. I believe in all the players of the squad," said Jesus after a 2-0 cup win over Moreirense on Friday.
He has been rotating his squad and will be boosted by the return of influential captain Luisao.
The centre back returns for his first Champions League match after a two-month suspension for physical aggression against a referee in a pre-season friendly in Germany.
Lanky Serb Nemanja Matic, who stepped up to the holding midfield role, is a doubt after picking up a knock during his man-of-the-match performance against Moreirense.