Mariano's late goal for Porto at Old Trafford last week was not the first time a last-gasp equaliser by the Portugese side had shocked Manchester United in the Champions League.
In 2004, Francisco Costinha's injury-time goal knocked Sir Alex Ferguson's side out of Europe - and saw a certain Jose Mourinho announce himself to the English public with a manic dash down the touchline to celebrate with his players.
Porto went on to win the 2004 competition but it was a night to forget for United fans.
But did it ultimately lead towards Ferguson's own European triumph in 2008 and his side's pursuit of five trophies this season?
That 2004 United side (below) looks poor on paper and was especially weak defensively because of the absence of Rio Ferdinand, who was suspended for missing a mandatory drugs test. The FA Cup was the only piece of silverware to arrive that season and things got worse - United won nothing at all in 2004/05 and only the Carling Cup in 2005/06.
Ferguson, not for the first time, rebuilt his team to win back the Premier League title in 2007 and 2008, and of course conquer Europe last season too.
Now United face a tough trip to Portugal and Porto's Estadio do Dragao on Wednesday where they will try to repair the damage caused by Mariano's goal in their 2-2 quarter-final first-leg draw.
Porto's 2004 Champions League-winning captain Jorge Costa feels United underestimated Porto in the first leg:
If they progress to the semi-finals, Ferguson's men could still end up winning an unprecedented five trophies this season - but what do you remember about five years ago, when things were not quite so rosy?
Do you remember watching Costinha's last-gasp goal, which ended up haunting United even more than they could have imagined. After all, do you think Mourinho would have ended up at Chelsea had he not won the Champions League that season?
You can find out what happened to the players involved at Old Trafford here:
But please share your memories and thoughts here too.
TEAM LINE-UPS: MAN UTD v PORTO (09/03/2004)
Man Utd: Howard, Phil Neville, Gary Neville, Brown, O'Shea, Fletcher, Djemba-Djemba, Butt, Giggs, Scholes, van Nistelrooy. Subs: Carroll, Ronaldo, Saha, Bellion, Kleberson, Solskjaer, Forlan.
Porto: FC Porto: Vitor Baia, Paulo Ferreira, Jorge Costa, Ricardo Carvalho, Nuno Valente, Alenitchev, Costinha, Maniche, Deco, Carlos Alberto, McCarthy. Subs: Nuno, Pedro Emanuel, Ricardo Costa, Jankauskas, Bosingwa, Ricardo Fernandes, Bruno Moraes.