Barcelona failed to secure its place in the knockout round of the Champions League on Wednesday as Celtic pulled off a major upset at Parkhead, beating the Spanish giants, 2-1.
Barcelona entered the contest having won its first three games in Group G to take a commanding lead at the top of the table.
However, Victor Wanyama's headed goal in the 21st minute from Charlie Mulgrew's corner kick gave Celtic fans hope.
The home side spent much of the match on the back foot, desperately defending their one-goal lead in an effort to shock the visitors.
Barcelona twice hit the woodwork with the team pressing for an equalizer, but 18-year-old substitute Tony Watt came off the bench to send Parkhead into delirium by scoring on the break.
Lionel Messi pulled a goal back for Barca in stoppage time, however the hosts held out for the win to move to within two points of the Catalan side at the top of the group.
Benfica takes over third place and remains in the hunt for a place in the next round as Oscar Cardozo scored two goals in the second half of a 2-0 win over Spartak Moscow in the group's other contest.
Manchester United maintained its perfect record with a 3-1 comeback win at Braga, which clinches the top spot in Group H for Sir Alex Ferguson's men.
A penalty kick from Alan in the 49th minute put the Portuguese side ahead, but Robin van Persie equalized 10 minutes from time after a goalkeeping error from Beto.
Wayne Rooney put United ahead in the 84th minute from the penalty spot, and Javier Hernandez sealed the win with a goal in stoppage time.
Galatasaray revived its hopes of reaching the next round as Burak Yilmaz scored a hat trick in his team's 3-1 win at CFR Cluj, moving the Turkish side into a tie with Cluj and one point clear of Braga.
Group E remains close at the top as Chelsea joined Shakhtar Donetsk on seven points after Victor Moses scored deep into stoppage time of a 3-2 home win for the Blues over Shakhtar, while Juventus is one point back of the leaders after thumping Nordsjaelland, 4-0.
Bayern Munich got a first-half hat trick from Claudio Pizarro en route to a 6-1 romp over Lille in Group F, moving Bayern to the top of the group along with Valencia, which got two goals from Sofiane Feghouli in a 4-2 triumph against BATE.