Celtic's most memorable Uefa Cup campaign came in 2002/03 when they reached the Seville final against José Mourinho's FC Porto, but perhaps their greatest result in the competition this decade came the following year when they toppled Barcelona.
Barça had now got their groove back after going four years without a trophy. The signing of Ronaldinho in 2003, rather than the emergence of Lionel Messi, was the catalyst for the success they enjoyed under Frank Rijkaard and Pep Guardiola as they would go on to finish ahead of Real Madrid in the 2003/04 Primera Liga.
However before their hegemony had begun, they were humbled by Martin O'Neill's Celtic. On what was the last glory night for the Bhoys under the Ulsterman's guidance, it was the one-time England international Alan Thompson who breached Barça.
Before the 59th minute goal Parkhead witnessed the usual barrage of dominance from its superior visitors. Ronaldinho, Javier Saviola and Luis García were all guilty of missing presentable chances before wannabe hardman Thiago Motta unwisely decided to punch Bobo Balde.
The incident wasn't forgotten and Celtic goalkeeper Rab Douglas and Motta were both sent off after a tunnel melee as the teams headed in for half-time. Then four minutes into the second 45 Saviola was given a straight red card for a shameless swipe at Thompson's leg.
Celtic made the man advantage count Stiliyan Petrov's direct cross was won brilliantly by Henrik Larsson, who nodded the ball down for Thompson to clinically finish past Victor Valdés.
Celtic held the Blaugrana to a 0-0 draw at Camp Nou for the return leg. Since Celtic's triumph, only Chelsea, Liverpool, Manchester United and Internazionale have eliminated Barcelona from European competition.