MILAN Porto must follow in Barcelona's footsteps and achieve a Champions League first on Tuesday if they are to overcome Juventus and reach the quarter-finals.
The Portuguese league leaders will have to claw their way back from a 2-0 home defeat in the first leg, something which has never been done in the knockout stage since Europe's top club competition was reformed in 1992.
Only two sides have even managed to overcome a single-goal deficit away from home in the last 25 years - Ajax Amsterdam against Panathinaikos in the 1995/96 semi-finals and Inter Milan against Bayern Munich in the round of 16 in 2010/11.
Juve's recent home record makes the task even more daunting.
The Serie A titleholders have not lost in their own stadium since their 1-0 defeat to Udinese in August 2015, a run of 45 games in all competitions.
In European competition, they are unbeaten in their last 20 home games since losing 2-0 to Bayern Munich in the Champions League in April 2013.
Porto, who have won their last nine league games and not conceded a goal in their last five, will not go quietly, however.
"We know it's going to be difficult for us after the result in the first leg. But a lot of things happen in football -- we've seen it all," said goalkeeper Iker Casillas on Facebook.
Casillas was almost certainly referring to Barcelona's remarkable achievement last week when they recovered from a 4-0 first-leg defeat to beat Paris St Germain 6-1 at the Nou Camp.
But the Portuguese league leaders could also look nearer to home for inspiration, having themselves won 3-0 away to AS Roma at the start of this season.
That win, their fourth in 13 visits to Italy, took them into the Champions League group stage against the odds after Roma had held them to a 1-1 draw in the first leg of the playoff tie.
It remains to be seen how Porto coach Nuno Espirito Santo, a firm believer in the idea a team is built from the back, will approach a game where his side will need to take the initiative.
"Our basis principle is defensive solidarity," he said after the 4-0 win at Arouca on Friday.
"Everyone has to defend, from the centre forward to the goalkeeper, so that we can get convincing wins. It demands a lot of work and a lot of concentration."
(Writing by Brian Homewood, editing by Pritha Sarkar)