As the United defence went AWOL in the dying stages of the first leg against Porto to allow Mariano to equalise, just minutes after Carlos Tevez looked to have secured victory, the Old Trafford faithful went silent.
At 2-1, the tie was very much in the balance, considering that Porto had one away goal. A 1-0 back in Portugal would send them through. So, for the game to eventually finish 2-2 must count as a mini-disaster. The result leaves Manchester United realistically needing a win over at the intimidating Estadio do Dragao.
A 2-2 draw would prolong the tie and send it into extra-time and possibly penalties. Anything higher than a 2-2 would also see Manchester United progress.
As Porto has recorded wins this season over the likes of Fenerbahce and Arsenal, and also managed to keep a clean sheet against Atletico Madrid, who have quite an array of attacking options, most neutrals might think that Porto have a great chance of qualifying for the semifinals.
After all, they just need to shut up shop at the back, like they did against Atletico, and hold on for the final whistle, right?
Easier said than done. Manchester United will take some stopping. Porto are faced with a little bit of a dilemma here. Should they look to defend, Manchester United will eventually score. Here's why.
Occasionally brilliant, often bumbling. A goalkeeper cut from the same mould that produced Heurelho Gomes, Fabien Barthez, and, of course, Massimo Taibi, Helton is hardly a keeper you would rely on to keep clean sheets.
While he can hardly be blamed for the two goals conceded by Porto in the first leg, one needs only to look at the previous round of matches, where he let a Forlan shot coming straight at him spill into goal, for proof that he really cannot be counted on.
Suspect when coming for crosses and quite awful decision-making mean that he is the weakest link in the Porto lineup, and I am sure Sir Alex Ferguson will be instructing his men to shoot on sight.
The Porto Defence
While not exactly poor defenders, they are rather slow. In the first leg, Manchester United did not test them fully, as they were pegged back by some brilliant Porto attacks. Now, with Manchester United needing to go all-out from the whistle, they will be stretched to the limit.
I predict they will struggle in the face of lightning-quick Manchester United counterattacks.
He will be a star in this match. There are two reasons for this. Firstly, he was rested for the league game against Sunderland, and as such, should be fresh and raring to go for this one.
Second, Ronaldo thrives whenever people boo him. His best seasons in England have come after the infamous incident in the 2006 World Cup where he got England favourite Wayne Rooney sent off, and that, of course, meant he became an object of hate back in England and at every away ground.
This being the stomping ground of his former club Sporting Lisbon's rivals, he is going to be roundly abused by Porto fans. And he will perform.
The brilliant Bulgarian is back, and I think he has been missed. He provides all sorts of opportunities for his teammates with his quick thinking and vision, much like how Bergkamp used to be the brains for Arsenal.
Tevez and Rooney will provide the legs, but should Porto look to shut up shop, Dimitar Berbatov will be there to pick the lock all night long.
So that means Porto cannot look to defend from the first whistle. However, should they adopt an attacking approach, they will be torn to bits on the counter. It's a lose-lose situation for Porto, and I cannot see Manchester United getting knocked out here.
Porto no longer have the element of surprise now, as Ferguson will not need to tell his men about the dangers of Porto's attackers. Without underestimating their opponents as they did in the first leg, and possibly without the air of complacency hanging over Old Trafford, I think Manchester United are clear favourites to advance.
I'm going to put my money where my mouth is, so if you fancy lining your pockets with a little extra money, consider a little flutter on Manchester United to advance to the semifinals, which is priced at £1.90 at bet365.com.