Celtic clinched a place in the knock-out phase of the Champions League with a dramatic win over Spartak Moscow.
Gary Hooper pounced on a defensive error to give them the upper hand, but Ari equalised with a deft finish.
With time running out, Georgios Samaras won a penalty, which was rifled in off the bar by Kris Commons.
Commons was carried off on a stretcher following a foul by Kim Kallstrom that earned the Swede a second yellow card, but Celtic claimed the win they needed.
That, coupled with Benfica's inability to beat Barcelona, ensured Celtic progressed beyond the group stage for the third time.
And it completed a glorious group campaign during which the team that started as fourth seeds recorded a famous win over the Spanish giants viewed by many as the best team in the world.
After a joyous Celtic Park erupted at the final whistle, a visibly moved Neil Lennon described his side's progress as a "momentous achievement".
It was, at times, a nervous encounter against Spartak and the visitors settled quicker, knowing they had a lot less riding on the outcome than their hosts, who began tentatively.
Indeed, goalkeeper Fraser Forster found himself scrambling to his right following a nice one-two between Kallstrom and Jose Manuel Jurado, but the Swede's placed shot crept just wide.
Celtic forced a couple of corners, but the opening goal arrived almost without warning.
Juan Insaurralde miskicked as he attempted to cut out Samaras's pass, allowing Hooper a sight of goal and that was all the striker required as he hammered it low past Sergei Pesyakov.
Spartak continued to play some nice football, Emmanuel Emenike looking menacing, but for all that, Forster was having a comfortable evening.
And there was almost greater comfort for the home fans on 32 minutes, when the ball broke to Commons at the edge of the box, but his shot flew a yard wide.
Celtic, by this stage, were snapping into tackles, with Scott Brown in inspirational form, but when the captain was loose with a pass on the edge of the Russian penalty area, there was a high price to pay.
Spartak broke upfield with great pace, and Emenike slipped away from three Celtic players before playing in Ari, who finished the move off with a cute chip over Forster.
The unease returned to Celtic Park, though the beginning of the second half brought fresh impetus from Lennon's side, with Samaras clipping the outside of Pesyakov's post from a Mikael Lustig cross.
Former Celtic winger Aiden McGeady made his entrance from the Spartak bench to warm applause from the home crowd.
However, Spartak were less composed during the second period and Celtic, sensing they had the initiative, went close through Commons and Efe Ambrose.
With 12 minutes remaining, it looked as though Celtic had the goal they required.
Commons swung in a corner from the left, Charlie Mulgrew rose to head towards the top corner, but Pesyakov threw himself at it and somehow flipped the ball over the bar.
Celtic continued to press and, when Samaras collected the ball inside the penalty area, Marek Suchy challenged him clumsily and referee Felix Brych pointed to the penalty spot.
Commons stepped up and blasted the ball in off the underside of the bar to put Celtic on the brink of qualification.
Both sides were reduced to 10 men as Commons was carried off following Kallstrom's tackle, the Spartak man following him from the field after his second booking.
However, it had no bearing on the outcome as Celtic saw out the final minutes, sparking jubilation at the final whistle.