Glasgow Celtic delivered a stunning 2-1 victory over Barcelona in the Champions League on Wednesday, rewarded for a disciplined defensive display against the European heavyweight and making the most of its rare attacks.
Victor Wanyama headed the Scottish champions in front in the 21st minute and teenage substitute Tony Watt rounded off another swift counterattack in the 83rd.
Four-time European champion Barca dominated possession but could only score in stoppage time when Lionel Messi found the net after being continuously thwarted by goalkeeper Fraser Forster.
Celtic, which won its only European title in 1967, is now just two points behind Barca with two games left.
"I think it was one of the greatest nights in the club's recent history," Celtic manager Neil Lennon said. "It was very poignant at our 125th anniversary. One, to play Barcelona in such a prestigious game and two, to win the game under huge difficulties with the squad decimated by injuries and illness.
"The players are heroes. They are heroes to me. I can't speak highly enough of their performance tonight and they will go down in the history books of the club as the team who beat probably the best team in the world."
Barca's first loss in Group G after three straight wins prevented it from securing early qualification for the knockout phase.
The reverse of the result in the Camp Nou two weeks ago, when Barca came from behind to win 2-1, ended the Catalan side's 12-match unbeaten run.
"It is not the first time we have lost a game like this and it won't be the last," Barcelona coach Tito Vilanova said.
Barca took just eight minutes to put Forster under pressure with Xavi Hernandez powering in a shot from outside the penalty area.
But Celtic was crowding out the visitors in defense and when the hosts finally found the space to launch a counterattack, they delivered.
Just like two weeks ago, Celtic took the lead by exploiting Barca's defensive frailties.
Wanyama rose above Jordi Alba to meet Charlie Mulgrew's corner and he headed past Victor Valdes.
"The first goal was important and gave us the energy to go on," Wanyama said. "We have been working hard at set pieces, we knew we were going to get one and we did it well."
Five minutes later, Celtic came close to stunning Barcelona again.
Another speedy break forward started by Kris Commons led to Adam Matthews delivering the ball into the penalty area, where Giorgos Samaras was unable to make a connection before Valdes saved.
Barca couldn't always get the space to find its rhythm but looked dangerous when it did.
An interchange with Andres Iniesta after beating three defenders saw Messi break clean through, but his effort was tipped over the crossbar by Forster.
The visitors weren't panicking in the search for an equaliser, with the passing carousel around the penalty area patient before Xavi found the space to launch a shot that couldn't match the quality of the buildup.
Alexis Sanchez was denied by the post before halftime from a header and, as Celtic continued to pack its defense, Forster was Celtic's assuring presence between the posts.
The English goalkeeper kept out a dipping shot from Messi and pulled off a double save to deny Alexis, diving low and then using his feet to block the follow-up.
Forster did even better to deny Messi from point-blank range, palming the ball away with a diving save after the Argentina forward's one-two with Jordi Alba ripped through the Celtic defense.
And there was an easy save to make when Messi sent a tame free kick straight at Forster.
Celtic went straight up the other end to score.
Forster's clearance went high over Xavi and fell straight at the feet of 18-year-old striker Watt, who lashed the ball straight past Valdes.
The closest Celtic had gone to extending its lead until then was Mikael Lustig heading straight at Valdes.
Barca never gave up hope of a second comeback in two weeks, but even Messi's late goal proved to be too late.
Forster finally was beaten only after he denied David Villa and Messi pounced to send the rebound into the roof of the net.