Celtic took a massive step towards the last 16 of the Champions League with an astonishing victory over Barcelona. They took the lead when Victor Wanyama rose majestically to head past Victor Valdes. Barcelona pressed for an equaliser, but Tony Watt came off the bench to give Celtic a cushion in the closing minutes. Lionel Messi tapped home in injury time, but Celtic held on to inflict Barca's first defeat of the season. It was a momentous victory for Neil Lennon and his men, banishing memories of the injury-time defeat in Barcelona a fortnight ago. Celtic Park was rocking at a decibel level previously reserved for the most meaningful of Old Firm derbies, but predictably the unflappable maestros of Barcelona paid the partisan crowd no heed as they quickly settled into their fluid passing game. It brought them the first opportunity of the game six minutes in, but Fraser Forster dealt easily with Xavi's shot despite a touch from Alexis Sanchez just in front of the keeper. Messi blazed over the bar from a promising position moments later as the pattern of play was quickly established. Alex Song picked up an early booking for pulling back Miku and a second late challenge on the same player might have cost him his place on the field after just 18 minutes with a more officious referee. Few inside Celtic Park had cause to debate that for long as the home side snatched the opening goal three minutes later. The source, as in the game at Camp Nou, was a Charlie Mulgrew set-piece - this time a corner from the right. His deep delivery was met forcefully by Wanyama, who outjumped Jordi Alba - the man whose late winner broke Celtic hearts two weeks ago - and headed high past Valdes to send the crowd into raptures. The manner of the goal again highlighted an aerial vulnerability in the otherwise practically flawless Barcelona make-up. They quickly resumed their relentless probing of the Celtic defence, almost finding an equaliser as Messi played a one-two with Andres Iniesta before rifling a shot off the top of the crossbar. The frame of the goal came to Celtic's rescue again as Alexis got on the end of a Dani Alves cross only to see his header come back off the post. And then Kelvin Wilson scrambled the ball off the line as an Alba cross caused hearts to flutter in the stands. Nonetheless, unlike in the previous meeting, Celtic held onto their lead until half-time and it was fully 11 minutes into the second period before Forster was meaningfully called into action, diving to his right to stop a curling Messi effort. Celtic made Valdes work from another corner, though Mikael Lustig's header lacked the power to really test him. Forster, sublime in Camp Nou, reproduced that form on the hour mark as he got down quickly to push away Alexis's well-struck shot from 10 yards and the keeper was promptly back to his feet to deny the Chilean on the rebound as well. Marc Bartra almost gifted Celtic a second goal, waiting on Valdes to come and deal with a cross ball. When the keeper chose to stay on his line, Mulgrew looked poised to volley past him, but Bartra recovered to block the shot. The Celtic fans bayed for a red card for Song midway through the half for another foul on Miku, but the referee again let him off. Forster pulled off another outstanding stop to scoop yet another Messi shot up and away and the Argentine also saw a free kick comfortably held with eight minutes remaining. The keeper dispatched the ball upfield, Xavi failed to cut it out and Watt showed composure beyond his years to bury it past Valdes. Messi ensured a nervy final few minutes as he scored at the start of injury time, following up after Forster had saved superbly again, but Tito Vilanova's side could not find another goal and Celtic and their supporters were left to celebrate long into the night.