Two goals by South Africa striker Benni McCarthy gave Porto a 2-1 comeback win in Portugal in the first leg of their first knockout round clash.
Juventus, beaten on penalties by AC Milan in the 2003 final, went down 1-0 at Deportivo Coruna after Albert Luque's first-half goal.
The evening's two other games produced 1-0 away wins, for Chelsea at VfB Stuttgart and Olympique Lyon at Real Sociedad, with both games decided by own goals.
South Africans were to the fore in Porto with Quinton Fortune putting United ahead after 14 minutes, only for compatriot McCarthy to equalise on the half hour.
SUPERB HEADER
The game seemed to be drifting towards a draw until McCarthy rose superbly to score with a long-range header in the 78th minute.
United's bad night was completed when captain Roy Keane was sent off three minutes from time for stamping on Porto keeper Vitor Baia
Manager Alex Ferguson thought the incident was accidental and was unhappy with what he considered the gamesmanship of the home team.
"It's the diving they do," he told Sky TV. We've seen it before from this team and it's unacceptable."
On the Keane incident he said: "Maybe it was a bit accidental and the goalkeeper has made a real meal of it."
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Porto coach Jose Mourinho said: "We had the ball, we had the chances, we were the better team it's just a pity we couldn't score more goals."
Deportivo were the only winners from the four Spanish teams left in the competition following Real Madrid's 1-1 draw at Bayern Munich on Tuesday.
They went halfway towards gaining revenge on Juve, who knocked them out of the second group phase last season, when Albert Luque capitalised on a blunder by France international defender Lilian Thuram to blast the only goal after 36 minutes.
The Spaniards deserved their lead against the shot-shy Italians and though they also dominated the second half, they failed to create many clear chances.
Chelsea, almost certainly out of the running in the premier league, remained on course to give Russian owner Roman Abramovich a handsome return for his $230 million player outlay after a first win for the club in Germany.
The decisive moment was an own goal by Fernando Meira in the 12th minute as the defender stretched to cut out a cross by Glen Johnson.
Both teams missed some decent chances while Chelsea goalkeeper Carlo Cudicini made several good saves.
RANIERI RELIEVED
However, Chelsea, who have won all five away games in Europe this season, kept the ball well to earn a much needed result for under-fire manager Claudio Ranieri.
"It wasn't easy after the two defeats against Arsenal," the Italian said after the league and FA Cup losses to their London rivals.
"After 20 minutes we showed our football but we were anxious and nervous before that."
"But my players don't believe in the newspapers, they believe in our project. I am the manager and we continue to work together."
Lyon's slice of luck came after 18 minutes when Sociedad defender Gabriel Schurrer scored an own goal as he tried to clear from midfielder Florent Malouda.
Sociedad had not lost at home in European competition since 1975 but found it hard going against the lively French visitors who should really have scored more.
Valery Karpin hit the bar for Sociedad while Malouda hit a post late on for Lyon.
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