SIR Alex Ferguson promised a “full throttle” display – but he was given a white knuckle ride as Porto gave his European champions an almighty fright.

Substitute Mariano’s 89th minute strike puts United’s defence of the trophy in a precarious position ahead of next week's Champions League quarter final second leg.

In truth it could have been much worse on a night when the Portuguese champions looked capable of blowing United away.

Carlos Tevez’ 85th minute goal looked like putting Ferguson’s men in control – even if it would have been cruel on the visitors – but Mariano’s stunner means United have it all to do in Portugal.

Ferguson had spoken of his side’s unique flair for the occasion in the build up to the clash and the ability to keep their tormented supporters on the edge of their seats right to the death.

But even he couldn’t have anticipated what they would serve up against the Portuguese champions.

Falling behind to Cristian Rodriguez’ goal after just four minutes, their defence of the trophy they won in Moscow last May, could have been as good as over by half time.

Only cartoonish defending from Bruno Alves gifted Wayne Rooney with an equaliser in a torrid first half.

Bidding to become the first manager to win back-to-back Champions League titles, Ferguson will know that it will take a much more convincing performance next Wednesday if his side are to progress to the semi finals.

A 1-1 draw was enough to see United knocked out the last time they faced Porto – and 2-2 draw is even more dangerous.

It was with Porto that Jose Mourinho’s legend was born, and their current coach, Jesualdo Ferreira will have caught the eye of suitors from across the continent with the way he took United on at their own game – and very nearly won.

Ferreira insisted attack was the best form of defence and he was as good as his word as he instructed his side to go for the throat.

Perhaps buoyed by the joy Villa had at Old Trafford on Sunday, Porto showed no fear on night when the Theatre of Dreams seemed as dumbstruck as United’s defence.

Still without Rio Ferdinand, who failed to recover from the groin problem he picked up on England duty, United at least had Nemanja Vidic back alongside Jonny Evans at the heart of the defence.

Nerves

But not even the Serb could settle his young partner’s nerves, with Evans suffering an evening to forget.

He may have been one of the discoveries of the season, but Evans’ indecision allowed Lisandro a shot on goal after only three minutes, which Edwin van der Sar was grateful to push away.

But just a minute later, the Northern Ireland international was culpable again when his weak clearance fell to Rodriguez.

The forward didn’t need a second invitation to head into the box and side-footed an effort past the stretching Van der Sar to stun Old Trafford.

United were shell-shocked too – and it wasn’t until Ronaldo rose to head a John O’Shea’s cross in the 13th minute that they looked anything like threatening themselves.

It says everything about Porto’s dominance that it took the most generous of gifts from Bruno Alves to settle the scores.

His blind back pass fell straight to Rooney, who clipped his shot over Helton and into the back of the net.

Even that wasn’t enough to rouse United from their slumber, with Porto still creating the better of the chances – Rodriguez and Lisandro coming close before the break.

Ferguson had his work cut out at half time, and when there was little response from his players he sent for Ryan Giggs to provide more of a cutting edge and composure in possession.

It prompted United’s best period of the match with Rooney almost catching Helton out with a chipped effort, while the Porto keeper had to parry a powerful header from Vidic.

Still the visitors remained threatening themselves with Lisandro forcing a fingertip save from Van der Sar.

It was time for cavalry and on came Carlos Tevez and Gary Neville for Paul Scholes and Evans respectively.

Neville almost had an immediate impact, crossing for Rooney, who failed to keep his glancing header on target in the last 15 minutes.

But it was Tevez – dropped to the bench after a toothless display against Villa on Sunday – who looked like being United’s saviour when he volleyed home Rooney’s flick on with only five minutes on the clock.

It looked like another late salvation for Ferguson’s men – but just as they had done to Villa, Porto stunned them with a last gasp strike.

Mariano, racing towards the back post, latched on to Lisandro’s inviting cross, flicking past Van der Sar.

It was edge of the seat stuff again at Old Trafford – and it could be another rollercoaster ride in Portugal next week.

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