The Swedish striker came off the bench after Ronaldinho had missed from the spot and substitute Chris Sutton had cancelled out Deco's brilliant first-half opener.

And Larsson made no hesitation in making his former worshippers pay by being involved in the build-up to Ludovic Giuly's goal before making sure of the points himself.

Celtic had bravely hauled themselves back into the match before Larsson's grand entrance having been outclassed by Frank Rijkaard's star-studded side in the first-half.

Barcelona's pace up front understandably made Celtic's defence nervous and last season's Nou Camp hero David Marshall needed to rush off his line quickly to clear the ball after Juliano Belletti had threatened to capitalise on Jackie McNamara's indecision.

Nearly everyone, including Ronaldinho, thought he had found the net in the sixth minute when Xavi played the ball back to him just outside the box and the Brazilian whistled a blazing left-foot rocket past the upright much to the relief of the home side.

Marshall again denied the visitors in the 11th minute when Eto'o teed up former Rangers man Giovanni Van Bronckhorst and the teenage goalkeeper did well to block his effort with his feet.

But there was nothing the youngster could do in the 20th minute as Barcelona did what they could not do last season and score.

Deco seized on a slack ball from Agathe and gave Ronaldinho the chance to tease the home defence before laying off the overlapping Portuguese star, who blasted a right-foot shot past the hand of Marshall and into the top corner of the net.

Barcelona were threatening to run riot and Marshall did well to save Ronaldinho's strike before Van Bronckhorst fired into the sidenetting.

German referee Markus Merk and his assistants were further incensing the Celtic team with some ridiculous decisions and then booked Juninho for remonstrating over one of them.

Camara was next to attempt the flamboyant roll over when he was cut down by Marquez which earned the Barcelona man a booking.

Celtic seemed to calm themselves down after a backs-against-the-wall start and Stanislav Varga should have forced Valdes to make a save in the 36th minute.

Alan Thompson curled one of his left-foot crosses into the area and despite being given too much room by the visitors he headed high over the crossbar from eight yards.

Barcelona threatened to score every time they went forward and Marshall again came to Celtic's rescue when he diverted Giuly's shot behind in the 43rd minute.

The Frenchman would have made it two just before the break, after more shoddy defending from Celtic, but Bobo Balde's outstretched leg squeezed the ball just wide.

Juninho became the player to pay for their first-half lesson as O'Neill decided to take him off at the break and throw on Sutton despite his lack of match fitness.

But Barcelona were handed a golden opportunity to double their advantage in the 55th minute when McNamara tripped the magical Giuly in the box after he had burst through following a great defence-splitting touch from Ronaldinho.

The Brazilian stepped up to take the spot kick himself but Marshall threw himself to his left and somehow clawed the ball behind for a corner with his right hand above him.

And Ronaldinho paid the price for that in the 58th minute when Celtic launched a rare foray forward.

Camara raced down the right and whipped in a great cross to the back post where Sutton acrobatically stretched out his boot to direct the ball in off the opposite post.

Rijkaard responded instantly to Celtic's surprise strike by throwing on Oleguer and Larsson for Ronaldinho and Marquez.

O'Neill also made a change by bringing on Valgaeren for Hartson before waving his hands at the crowd to make more noise to continue to unsettle the visitors.

Celtic were finishing the stronger and Valdes pulled off a brilliant save to tip Petrov's right-foot shot over the top.

It was Barcelona's turn to look rattled and Belletti went agonisingly close to putting the ball into his own net as he clipped the ball past his post with Thompson lurking.

It was inevitable though that Larsson would do something against his former club and he was involved in the build-up to snatch the lead for Barcelona against the run of play.

He found the overlapping Belletti and he centred for Giuly to fire low past Marshall from the edge of the area.

McNamara was stretchered off as he tried to block his effort but it was to go from bad to worse for the Scottish champions.

Larsson seized on a short header back from Thompson to take the ball around Marshall and steer the ball home to hurt those that just last season cherished him, and with a goodbye and embrace for former strike partner Sutton he left Parkhead again