Sir Alex Ferguson has set his side the task of becoming the first English team to defeat FC Porto on their own ground after Manchester United were held to a 2-2 draw at Old Trafford.
It seemed United were going to get away with another below-par display, just as they did against Aston Villa at the weekend, when Carlos Tevez gave them an 85th-minute lead in their Champions League quarter-final.
But poor defending allowed an unmarked Mariano to finish off Luisandro's cross a minute from time to give Porto the draw they deserved.
"No British team has won there, so it is going to be difficult," admitted Ferguson. "But we are used to being first and we need to be first again because we have to win."
Porto have only recorded five wins from their 11 previous home encounters against English teams, which does give Ferguson some hope.
However, they held Atletico Madrid comfortably enough in the last round after recording exactly the same scoreline in their first meeting with the highly rated Spanish outfit.
And Ferguson accepts United have no-one but themselves to point the finger at for the mess they find themselves in.
"We only have ourselves to blame," said the Red Devils chief. "To get a goal late on is quite a normal situation for us. But the one we gave away was absolutely terrible.
"You couldn't say it was a great goal or a manufactured goal but we just made the kind of mistake we are making at the moment."
Ferguson confirmed the situation will get worse before it gets better as Rio Ferdinand is almost certain to miss Saturday's trip to Sunderland with the groin injury which sidelined him this evening.
He will be joined on the sidelines by Jonny Evans, who limped off midway through the second-half and now faces a rush to be fit for the second leg next Wednesday.
"Rio was nowhere near being fit tonight, so it is difficult to see him being fit for Saturday," said Ferguson.
"Jonny should be okay in a week but he is a 21-year-old lad and this is what happens when you play two big games in three days."
The tired performance was perhaps understandable given Ferguson gambled on playing Aston Villa on Sunday rather than Saturday because he would have had no time to get any training into some of his squad, including Tevez.
Porto were fast out of the blocks too, with Cristian Rodriguez putting them ahead after just four minutes.
Wayne Rooney profited from a catastrophic error by Bruno Alves but United knew they could easily have been behind before the dramatic late ending.
Porto coach Jesualdo Ferreira had nothing but praise for his team, who were decidedly unlucky to find themselves behind after dominating the first half.
However, he is taking nothing for granted despite Porto's impressive record on home soil against English opposition, which includes three previous encounters with United, the last a victorious one under Jose Mourinho in 2004.
"The score is very good but we need to convince the players they can do better," said Ferreira.
"United will probably play in a different style because they either need to win or get a very high scoring draw."
The 62-year-old could take immense satisfaction from both the way his team played and their refusal to accept defeat when Tevez's superb finish looked as though it had won the game for United.
"It is good to know my players have the capacity to do that," he said.
"We were delighted to reach the quarter-finals. Now we need to find out if we can do even better."