Marvin Andrews helped Trinidad & Tobago to the World Cup Finals last week and insists Rangers must show the same belief going into tonight's game to secure a favourable result.
The Light Blues are severely depleted for this clash, with several key players including Nacho Novo, Thomas Buffel, Dado Prso and Julien Rodriguez missing through injury, but are still well poised in Group H to progress through to the next round.
A victory in the Dragao Stadium for Alex McLeish's side, combined with an Inter Milan win, will guarantee Gers make it into the knockout stage - a first for any Scottish Club.
But even a draw would keep the club's dreams alive of playing in Europe after Christmas and Andrews is desperate to help the Light Blues turn their season around.
Rangers' European form has been the highlight of a disappointing term so far and avoiding defeat in Portugal will be another fine result.
It will be an extremely tough challenge for the visitors but Andrews is remarkably upbeat.
The odds of Trinidad & Tobago qualifying for next summer's World Cup were stacked against Leo Beenhakker's side at one stage of the campaign, but Marvin admits the players never gave up.
Victories against Guatemala and Mexico in the final two matches secured a play off place, before the Soca Warriors pulled off a brilliant win in Bahrain to book their place in Germany.
Tonight Rangers must adopt a similar attitude and Andrews insists this could just be the match to turn fortunes around.
He said: "We have to keep believing and if we do there is every chance for us to make it through to the next phase.
At one point no one had the slightest hope that Trinidad & Tobago would qualify for the World Cup but the reality is that we made it.
"At the moment we are not having much luck here at Rangers but if we keep the faith then we will come out of it stronger.
"These things happen for a reason and if we stay united as a squad then I know things are going to come good for us.
"We were all disappointed about the Old Firm result but we have tried to learn from the mistakes and put the SPL to one side for now.
"We're now looking forward and concentrating totally on the Porto game, which is huge for us.
"We know a win can put us into the next phase and that is what we are aiming for.
"Nothing good comes easily and if we want to get to the next stage we have to go to places like the Dragao stadium and win."
Andrews will line-up alongside Sotirios Kyrgiakos tonight and is aware the defence must be at its absolute best to keep out Co Adriaanse's men.
Having lost the first encounter at Ibrox, Porto must win this game to give themselves a chance of extending their European run and Marvin believes that factor may be an advantage for Gers.
He added: "They need a victory more than us and if we can leave with a draw it would be a good achievement.
"We can take confidence from the first game because we have proved we can beat them, but we know this match will be very different.
"They'll have their fans behind them and will want revenge.But we know what to expect and are mentally ready for this battle.
"Things haven't been going for us in the SPL, although I don't think we have been playing particularly badly.
"We have to forget about that and focus on changing our fortunes against Porto tonight."