BARCELONA, Spain -- Spain left back Jordi Alba scored in the fourth and final minute of stoppage time for Barcelona to come from behind and beat Celtic 2-1 in the Champions League group stage on Tuesday.
Alba glanced Adriano's curling pass into the box to deflect the ball beyond goalkeeper Fraser Forster, who starred throughout the match and made brilliant saves to deny Lionel Messi and Alexis Sanchez in the closing stages.
"It's gut-wrenching," Forster said. "Everybody's devastated."
Celtic opened the scoring at the Camp Nou stadium through Giorgos Samaras' 18th-minute header that deflected into the net off Barcelona defender Javier Mascherano.
The Catalan club equalized when Andres Iniesta finished a slick combination with Xavi Hernandez to score his first goal of the season in the 45th.
Barcelona remains perfect in Group G with nine points from three games, while Celtic has four points. Spartak Moscow has three points after a 1-0 win over Benfica, which has one point.
The Spanish league club can secure its place in the knockout stages with a victory at Celtic in the next round of matches in two weeks' time.
"It feels good because it would have been pretty unjust if we hadn't won the game," Andres Iniesta said. "We're in a very good situation right now. But until we secure it we shouldn't talk about it."
Barcelona coach Tito Vilanova surprised by starting untested 21-year-old Marc Bartra in the center of defense alongside Javier Mascherano as Gerard Pique and Carles Puyol are injured. Alex Song played in the holding midfield spot with Sergio Busquets suspended.
"No nerves, I've been preparing a long time for this moment," Bartra said.
Sanchez nearly chipped the ball into the net after two minutes. But Bartra had the best of Barcelona's early chances, forcing Forster into saving his header only moments after Celtic had scored.
Samaras had to be replaced in the 41st with a left ankle injury, and not long after Messi found Iniesta moving into the area to slot home the equalizer.
Messi grazed the crossbar with a couple of free in his best chances of the first half but the hosts just couldn't crack Celtic's stingy defense.
Celtic midfielder Victor Wanyama headed a 53rd-minute corner wide of an open goal as the visitors persevered. But Barcelona poured forward to create several chances, with substitute David Villa hitting the post in the 90th.
In the end, it was Alba who popped up with another key goal, stunning Celtic coach Neil Lennon.
"We're hurt, disappointed and upset. We leave without a point but we take positive conclusions away with us," Lennon said. "We surprised a lot of people who thought we wouldn't have a chance."
Information from The Associated Press was used in this report.