Douglas' absence meant a baptism of fire for 19-year-old goalkeeper David Marshall and with the match tied at 0-0, bringing an inexperienced keeper into the game seemed to have handed the upper hand to Barcelona. However, with tensions still running high after the break, Barca's Javier Saviola was given his marching orders after kicking out at Alan Thompson and the balance swung in favour of the home side.
On 59 minutes Celtic took their chance when Stilian Petrov fed the ball on to Henrik Larsson who knocked the ball down to Thompson. After missing a chance in the first half, this time the Englishman did not miss and slammed the ball into the back of the net to make it 1-0. Barcelona were left to rue missed opportunities from Phillip Cocu, Ronaldinho and Saviola in the first half, and with only nine men on the pitch in the second their luck did not improve, as Ronaldhinho failed to find the back of the net again midway through the half.
Soon afterwards Larsson had a chance to stretch the Celts' lead but his shot from the edge of the area went just wide. Barcelona, and in particular Ronaldinho, showed signs of brilliance in the second half, but the Celtic defence was up to the task of protecting Marshall and they clung on to the end to take a one-goal lead into the second leg at the Nou Camp.
Celtic: Douglas, Varga, Balde, McNamara, Agathe, Lennon, Petrov, Pearson, Thompson, Larsson, Beattie
Subs: Marshall, Sylla, Lambert, Wallace, Smith, Kennedy
Barcelona: Valdes, Reiziger, Puyol, Oleguer, Gabri, Cocu, Xavi, Motta, Ronaldinho, Luis Garcia, Saviola
Subs: Rustu, Marquez, Overmars, Gerard, Quaresma, Iniesta, Oscar Lopez
Referee: Wolfgang Stark (Germany)