United missed a golden opportunity to qualify for the last 16 when they suffered a shock 1-0 loss to the previously winless FC Copenhagen thanks to goal from Swedish striker Marcus Allback.
Manager Sir Alex Ferguson was left defending his decision to field a weakened team after his side ended their seven match unbeaten streak.
"We had a team that was easily capable of winning the match without question and we controlled it most of the night," said the Scotsman, who will celebrate his 20th anniversary in charge of the club on November 6.
"I don't think we should concern ourselves with the team we played. We should concern ourselves with losing a bad goal from a corner."
Copenhagen coach Stale Solbakken couldn't hide his pride for his players who kept alive their hopes of reaching the knockout stages.
All stand for Allback
"Some of them could barely walk in the last ten minutes but still we managed to keep it tight after we scored," he said.
Former United midfielder and now Celtic Gordon Strachan could only watch as defender Gary Caldwell had a horror first half to hand three points to Portuguese side Benfica.
The Scottish defender scored an own goal after ten minutes before an misplaced header teed up Nuno Gomes for his side's second.
A strike by substitute Andrei Karyaka in the 76th minute completed the rout and brought the Portuguese club to within two points of the second-placed Glasgow club with two games remaining.
Arsenal manager Arsene Wenger was at his revisionist best when his side accumulated an astonishing set of blunders in front of goal to finish with a scoreless draw with CSKA Moscow.
"I feel that was the best Champions League game I have seen in my time at the club," he said, somewhat strangely.
"We put them out of position six or seven times in the first half and normally the score in this game is 7-0.
"There were lots of positives. We dominated them by miles and there was at least a division between the teams."
A division perhaps, but not a winning goal.
Joining Arsenal on seven points in Group G was FC Porto after they beat Hamburg 3-1 in Germany as the hosts continue to hunt for their first point of the campaign.
Group E sorted
While British sides will rue missed opportunities other sides took theirs as both Lyon and Group E rivals Real Madrid qualified for the next stage with 1-0 wins over Dynamo Kiev and Steaua Bucharest respectively.
Lyon, though, were more impressive than the rather faded Spanish giants who took the points after one of the strangest own goals ever from from Banel Nicolita after his hopelessly inaccurate back pass rolled into an open goal.
Banel Nicolita: A banal moment
In Italy AC Milan coach Carlo Ancelotti labelled Kaka "the best player in the world" after his hat-trick in the rossineri’s 4-1 hammering of Anderlecht.
The Italians are now top the group, while Lille's chances of securing second took a hit when they lost 1-0 to AEK Athens.
It was the Greeks first Champions League victory in 22 matches.