Recap the action below with Sports Mole's blow-by-blow text coverage of events at Parkhead.
7.19pmCeltic starting XI: Forster, Lustig, Ambrose, Wilson, Matthews, Commons, Wanyama, Ledley, Mulgrew, Miku, Samaras
7.20pmCeltic subs: Zaluska, McCourt, Herron, Fraser, Kayal, Watt, McGeouch
7.21pmBarcelona starting XI: Valdes, Alves, Mascherano, Bartra, Alba, Song, Xavi, Iniesta, Messi, Sanchez, Pedro
7.22pmBarcelona subs: Pinto, Pique, Montoya, Fabregas, Dos Santos, Villa, Tello
7.26pmNeil Lennon's men are without topscorer Gary Hooper, who has a hamstring problem. On-loan Getafe forward Miku partners Georgios Samaras in attack. Captain Scott Brown misses out through illness.
7.31pmMeanwhile, Barca boss Tito Vilanova has resisted the urge to rest three-time Ballon d'Or winner Lionel Messi. The Argentina forward is part of a three-pronged attack, which also includes Alexis Sanchez and Pedro. Gerard Pique, Cesc Fabregas and David Villa all start on the bench.
7.37pmCeltic celebrated their 125th anniversary yesterday and Lennon is expecting tonight's match to be "a great occasion".
7.38pmLennon: "It is a great occasion for the club, our anniversary and something we are very proud of. I think it will be a very special evening.
7.39pm"How do you solve a problem like Barcelona? You have to play at your very best, you have to be fully concentrated with great intensity and sometimes even then that is not enough.
7.40pm"But certainly with a full house I am sure the neutrals will enjoy the atmosphere and the energy that our supporters bring and it should be a great night for the club. I am hoping that the players do themselves justice on the night."
7.41pmThe Celtic fans are certainly doing themselves justice so far. The Stadium is a complete sell-out and a rousing rendition of 'You'll Never Walk Alone' is reverberating around the ground.
7.42pmThe players enter the pitch, as the famous Champions League anthem sound. The handshakes are underway.
7.44pmTonight's referee is 39-year-old Dutchman Bjorn Kuipers.
0minMr Kuipers blows his whistle and the match kicks off amid huge noise from all four stands of this famous stadium.
4minCeltic have matched Barca in terms of possession so far. The Hoops now have a free kick 30 yards from goal, which Charlie Mulgrew will take.
5minDespite both centre-halves going forward for the set piece, Mulgrew elects to go short. The cross eventually comes in from the Scotland wide man, but it is poor and easily dealt with.
6minChance for Barca! Mulgrew's poor defensive header falls to Xavi on the edge of the area. His volley at goal flicks off Sanchez, before being well gathered by goalkeeper Fraser Forster.
8minChance for Barca! Alba finds Messi in space 10 yards out, but the Little Maestro fires over the bar with his left foot.
13minYellow card for Alex Song. The Cameroon defender is bamboozled by a clever piece of skill from Miku on the halfway line and pulls the Celtic forward to the ground.
18minSong commits another foul on Miku - this time a clumsy trip inside the Celtic half. He escapes a second booking but he is taking unnecessary risks!
21minCorner to Celtic. Mulgrew to take from the right.
21minGOAL FOR CELTIC - Victor Wanyama - Celtic 1-0 Barcelona
21minGreat inswinging cross by Mulgrew to Wanyama, who rises at the far post to head home a simple goal. What a start for the Scottish champions!
25minCeltic have barely touched the ball since they broke the deadlock. The crowd are booing loudly in an attempt to unsettle the visitors.
26minDani Alves's long-range effort deflects off Mulgrew. Corner to Barca.
27minChance for Celtic! The Hoops clear the corner and launch a dangerous counter-attack, which ends with Adam Matthews's low cross from the left being dived upon by Victor Valdes. Samaras was in close attendance, waiting to pounce.
30minBarca hit the Woodwork! Andres Iniesta pokes the ball through to Messi, who, on the turn, fires a powerful left-foot strike against the crossbar from 15 yards.
36minBarca hit the Woodwork again! Sanchez gets up above Lustig and meets Alves's deep cross with a placed header, which flicks wide off the post.
41minBarca go close! Pedro fires the ball low across the six-yard box and Celtic just manage to hack clear.
42minMiku is shown a yellow card for an unnecessary foul on Marc Bartra.
Half timeHT: Celtic 1-0 Barcelona
8.36pmCeltic miraculously lead at the break. The Hoops have frustrated the La Liga giants so far, but obviously this game is far from over. Barca are undefeated in their previous 18 Champions League group games.
8.40pmThe Catalan side have dominated possession with an 85-percent share of the ball. Celtic's goal came from their only shot, while Barca have recorded 10 efforts at goal. However, Forster has only had to make one save.
8.45pmThe players are back on their field and the second half is moments away.
46minCeltic get the game back underway. Neither side has made any substitutions during the interval.
49minIniesta plays the ball wide to Alves, whose whipped cross is poor and evades the head of Messi.
51minBarca go close! This time Alves's cross is better and Pedro's header just skims the top of the net.
53minAlves gets in down the right again, but he is halted by a superb sliding tackle from Matthews in the penalty area.
54minMulgrew dispossess Messi deep inside the Celtic half and then drives forward, playing a one-two with Samaras, before being stopped by a good tackle from Song.
56minMessi cuts inside onto his left foot and curls an 25-yard effort at goal, which Forster does well to hold.
58minCorner to Celtic on the left.
59minThe corner is taken short to Mulgrew. He crosses to the back post, where Lustig heads straight at Valdes.
62minBarca go close! Forster makes an inspired double save to twice deny Sanchez from close range - first with his hands and then his feet.
64minChance for Celtic! A communication failure between Bartra and Valdes allows Mulgrew to sneak in at the far post. The Celtic man very nearly makes a telling connection to Efe Ambrose's long pass, but his shot is well blocked.
66minSubstitution for Barcelona - Villa replaces Sanchez.
67minJordi Alba is shown a yellow card for dissent.
68minLucky escape for Song! The former Arsenal midfielder, who has already been booked, goes to kick the ball but hacks straight through Miku. A free kick is given, but no card.
70minBarca go close! More magic from Forster as Messi shoots first time from Alba's pull-back, only to be denied by a super diving save from the Celtic keeper.
71minDouble substitution for Barcelona - Fabregas and Pique replace Song and Bartra.
73minSubstitution for Celtic. Lustig, who has picked up a knock, is replaced by Tony Watt. The 18-year-old is making his Champions League debut.
79minVilla fires wide from long range.
79minSubstitution for Celtic. Biram Kayal replaces Samaras.
83minGOAL FOR CELTIC! - TONY WATT - CELTIC 2-0 BARCELONA.
83minThe teenager produces the coolest of finishes one-on-one, slotting the ball low across Valdes from eight yards. What a way to introduce yourself to the rest of Europe!
87minChance for Celtic! Watt chases down a long ball and gets in behind the Barca backline again, before going to ground under pressure from Javier Mascherano just outside the penalty area. No free kick is given, but Mascherano could easily have been sent off for that.
90minFour minutes of added time go up on the fourth official's board.
90min+1GOAL FOR BARCELONA - Lionel Messi - Celtic 2-1 Barcelona
90min+1Forster does well to parry Villa's initial effort, but Messi slams home the rebound from six yards.
90min+2Celtic let a two-goal lead slip at Dundee United on Saturday. It isn't going to happen again, is it?
90min+3The ball goes out for a goal kick to Celtic and the crowd go wild. Almost there!
Full timeFT: Celtic 2-1 Barcelona
9.45pmWhat a result for Celtic! The Hoops must be handed great credit for their positivity. Yes, they enjoyed a fair slice of luck, with Barcelona twice striking the woodwork, however the La Liga giants can count themselves fortunate to finish the game with 10 men. Alex Song and Javier Mascherano were both lucky not to be sent off.
9.49pmThe other match in Group G has finished Benfica 2-0 Spartak Moscow, meaning that Celtic move three points clear in second place. Meanwhile, Barca remain top with nine points.
9.54pmTonight's man of the match was, without question, Fraser Forster. The former Newcastle United goalkeeper made seven saves to keep his side in front, including a vital double stop to deny Alexis Sanchez.
9.57pmHere are the rest of tonight's vital statistics from Parkhead...
Possession (percent):Celtic 16-84 Barca
Shots:Celtic 5-25 Barca
On target:Celtic 3-8 Barca
Fouls:Celtic 11-8 Barca
Corners:Celtic 2-7 Barca
10.10pmThat concludes tonight's coverage. Goodnight.