The Scottish champions' stuttering domestic form may have opened up the SPL title race, but it is their form in Europe that could make real waves.
Omens favour faltering Celtic in Champions League chase
Travel is supposed to broaden the mind. In which case, Celtic's horizons must have been broadened beyond belief. They are living out the football equivalent of Gulliver's Travels and, strangely, seem equally effective in both of the wildly differing worlds they inhabit.
They are sport's answer to Lemuel Gulliver, Jonathan Swift's famous character who was a giant in Lilliput and dwarfed in Brobdingnag.
With Glasgow rivals Rangers demoted to Division Three and, officially at least, a different club, Celtic are Scotland's sole superpower. They are also European underdogs, beginning their Champions League group as rank outsiders.
Yet they have flourished as minnows and floundered as overwhelming favourites. They lead the SPL, supposedly a one-horse race, by a solitary point. But should Barcelona beat Benfica at Camp Nou tonight, a point for Celtic will secure their place in the Champions League's last 16.
It is an improbable tale of continental heroics and domestic stumbles. They beat Barcelona and promptly drew with St Johnstone. They warmed up for tonight's game against Spartak Moscow by failing to beat the part-timers of Arbroath in the Scottish FA Cup.
And yet that may not bode badly.
"We will rise to the occasion," vowed manager Neil Lennon. It is what they have done so far. Europe has become the priority, the obsession for Celtic, just as it was almost half a century ago when they also seemed assured of winning the league title.
They are challenging the widespread perception that the Scottish club game is in terminal decline by closing in on a magnificent achievement.
They have already recorded one. Beating Barcelona at Celtic Park ranked second only to the 1967 European Cup final victory, according to Kenny Dalglish, one of the club's greatest players. They won with just 16 per cent of possession but with limitless quantities of spirit and determination in the special atmosphere of Celtic Park.
It was a night when Tony Watt, the 18-year-old substitute who scored the decisive goal, overshadowed Lionel Messi, an £80,000 (Dh470,400) signing upstaging a man with 84 goals in 2012.
The evening made the boy wonder a Bhoy. "The Celtic fans deserve to be in Europe," Messi said. "They have been amazing in both games we played them."
In both, Celtic were bold enough to select two forwards. Despite their record of struggling away in Europe, they were not condemned to defeat until Jordi Alba's 94th-minute goal in Spain. They beat Spartak in Moscow. And a traditional club have done so with very modern methods.
When Celtic conquered Europe 45 years ago, it was with 10 players born in Glasgow and neighbouring Lanarkshire. The closest to a foreigner was Bobby Lennox, who came from Ayrshire, some 30 miles away. Now their progress is reward for intelligent recruitment.
While Victor Wanyama chose 67 as his squad number to celebrate the Lisbon Lions, the £900,000 buy from the Belgian side Beerschot is Kenyan. Sadly for Celtic, he is suspended today but the Israeli Beram Kayal is another inspired import. So, too, the Honduran Emilio Izaguirre.
Besides the obvious Scottish contingent, there is a Spaniard, a Swede, a Greek and an English goalscorer and goalkeeper.
They have enabled the cosmopolitan Celts to take on the more fancied. Spartak belong to Russia's moneyed classes but they are already eliminated and without a manager. They will encounter a wall of noise at Parkhead. Celtic, the giants turned giant-killers, are on the brink.
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