On a fretful evening at Parkhead – where both teams finished with 10 men – Celtic garnished their 150th European Cup tie with a historic victory over Spartak Moscow, courtesy of Gary Hooper's first-half strike and Kris Commons' late penalty.
Ari's clever chip for an equaliser before the interval was the cause of prolonged uneasiness amongst the Hoops support until Commons pushed them over the line, with scant help from Barcelona, who played a reserve team at home to Benfica.
Striker Gary Hooper opened the scoring in the 21st minute when he capitalised on a mistake by Spartak defender Juan Insaurralde but that lead was cancelled out in the 39th minute by Ari, after good work by the impressive Emmanuel Emenike.
However, the Scottish champions were not to be denied and, after defender Marek Suchy conceded a penalty in the 80th minute for a clumsy barge on Georgios Samaras, up stepped Commons to slam the ball in off the bar.
To add to Neil Lennon's accomplishments, Celtic have now beaten opponents home and away in the group stage for the first time to amass 10 points – the highest total achieved on the four occasions when a Scottish club has reached the last 16 of the Champions League.
The Hoops had to fight their way through two qualifying rounds and were then unfancied when drawn alongside the Russian club, Benfica and Barcelona.
The Scottish champions went in to the game knowing they would qualify for the knockout stages only if they got a better result against Spartak, consigned to the bottom of the table, than Benfica got in the Nou Camp.
All the big guns were back for Celtic's most important game of the season.
Fraser Forster, Kelvin Wilson, Commons, Hooper and Samaras were five of the nine changes the Hoops boss made to the makeshift team which started in the 1-1 home Scottish Cup fourth-round draw against Arbroath on Saturday.
Tidings from the Nou Camp were being relayed long before kick-off and anxiety was induced with the news that Tito Vilanova had named a Barca side that was skeletal compared to the frighteningly formidable array faced by Celtic both home and away.
Although Lionel Messi had come within a single goal of Gerd Müller's calendar year record of 85 in 1972, the Argentinian striker was on the bench against Benfica.
Lennon, meanwhile, was glad of the presence of Emilio Izaguirre, after an early recovery from injury, but had to make up for the absence of the suspended Victor Wanyama, his most influential midfield operator in this European campaign.
Commons was extremely fortunate not to be cautioned for planting his studs into Jose Jurado's ankle – an incident that exposed Celtic's edginess in an atmosphere that did not duplicate the cacophony heard when Barcelona came to town.
Ominously, too, Emenike looked immediately dangerous, breaking at speed and working the spaces in the Celtic back line.
With nothing to lose, Ari and Jurado pushed up alongside Emenike to shred the home support's nerves even more.
Kim Kallstrom, too, found room to step forward from his deep-lying role for a placed shot that swept wide and when Wilson escaped scot-free for a lunge that caught Emenike just outside the box, it was abundantly clear that Celtic badly needed to restore their composure.
The wish was father to the deed, with Insaurralde playing midwife. The Argentinian tried to cut out a crossfield prompt from Samaras but made a hash of the contact to divert the ball straight into the path of Hooper, who made another 15 yards before firing low and precisely between Sergei Pesiakov and the left-hand post.
Even then, Wilson was profoundly grateful for help when he was outwitted by Emenike inside the box for a Spartak corner.
But there was no such succour for Efe Ambrose when he allowed his fellow Nigerian to stride across the edge of the Celtic penalty area to feed Ari, cutting in from the right behind Izaguirre, and the Brazilian scored his first Champions League goal with a chip that crossed the line despite Wilson's desperate attempt to head clear.
The issue now hung on whether Celtic could regain their lead or be obliged by a goal for the home team in the Nou Camp.
Yet it was Spartak who began to push higher up the field and it took a wholly unnecessary foul by Suchy to swing the pendulum back in Celtic's favour nine minutes from time when the centre-back strongarmed Samaras off the ball when the Greek had his back to goal, wide in the box.
Commons stepped up to face Pesyakov and thrashed the ball past the giant goalkeeper, via the underside of the crossbar.
But then a brutal challenge by Kalstrom – who was dismissed for a second yellow – saw Commons stretchered off.
His departure meant Celtic, who had used all their substitutes, playing five minutes added-time also with 10 men but by then the Celtic midfielder had contributed to another remarkable passage in the club's chronicles.
Still, a sense of anxiety had to be overcome before Celtic were able to celebrate. Even on a night of great tension, minds wandered from the play here.
The home side had to better Benfica's scoreline at the Camp Nou to progress to the knockout stages, but that game finished 0-0 before full-time at Parkhead.
Only seconds passed before the referee blew for full-time, though, confirming Celtic's progress, and the East End of Glasgow erupted. (© Daily Telegraph, London)