Brazil goalkeeper Dida threw a slippery ball into the net in the 89th minute to hand Leeds United a win.
A speculative drive straight at Dida by midfielder Lee Bowyer was dropped into the net when he tried to palm the ball away in difficult conditions.
Bowyer was the first player to take pot luck in the wet conditions and it paid off for Leeds with the killer goal that put a defence-mided Milan side to defeat.
These two teams cancelled each other out in a sodden Yorkshire encounter.
Leeds United showed better attitude and determination than against Barcelona last week when they backed off and showed far too much respect to the Catalan team.
They were quicker into the tackle and passed the ball well to test the Milan defence. Leeds manager David O'Leary ordered the Elland Road pitch to be narrowed by nearly two metres in the summer and Milan failed to get in the wide possession to supply chances for Andriy Shevchenko who was kept quiet with Danny Mills and Michael Duberry both playing well in the first half.
Milan have never won in England and looked content with a draw in a first half that seldom caught the imagination. The rain and heavy pitch also helped to reduce Milan's ambitions to raid forward.
The Italians began with an adventurous 3-4-3 formation but two strikers were regularly pulled back to leave Shevchenko alone.
Leeds almost fell behind in the 4th minute when Thomas Helveg collected a loose ball on the right and cut inside but his shot from an unchallenged position hit the side netting.
Eirik Bakke returned to the team after injury and came close with an 18th minute shot which Dida saved low and the same player sent a header over the bar only seconds later.
Bierhoff and Shevchenko lacked any mobility in the first half and fluffed a great chance in the 77th minute when the German ran off side when Shevchenko had broken through on the right hand side of defence.
Shevchenko had earlier forced a save from the edge of the area when he ran and drove at goal for Nigel Martyn to tip over the cross bar in the 65th minute.
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