There were plenty of shredded nerves by the end. Porto love a late goal and Manchester United rarely make life easy for themselves in Europe, but come the final whistle at the Estádio do Dragão last night, Sir Alex Ferguson was able to reflect on a job well done. His team finally seemed to rediscover, if not an aura of invincibility, then certainly some of the self-belief that they have been so painfully lacking in more recent weeks.

A corner turned? Who knows. We should have a clearer idea a week from now, when United will have played Everton in their FA Cup semi-final at Wembley and Portsmouth at home in the Barclays Premier League, but by becoming the first British team to win in Porto, courtesy of Cristiano Ronaldo’s sixth-minute wonder strike, the European champions sent out a marker of sorts to suggest that there is plenty of life in the old dog yet.

Arsenal will certainly beware the wounded animal. Ferguson’s reward for this victory, in his 150th Champions League match as United manager, is a mouthwatering semi-final showdown against that great old adversary of his, Arsène Wenger. Their rivalry may not be what it once was, but if ever there was a tie that could rekindle old fires, it is this, and given the cavalier tendencies of both teams, it is a contest that will be almost impossible to call.

For the moment, though, Ferguson will just be relieved that United have negotiated a tricky passage against a Porto team you sensed never really believed they could complete a job they had half done by earning a commendable 2-2 draw at Old Trafford in the first leg last week.

A little more conviction and the game might have taken on a different hue, even if they did give United one or two frights late on, but Ferguson will hope that this serves as a springboard to better things after an almighty wobble that threatened to derail their season.

United certainly looked far more assured in defence, despite Edwin van der Sar flapping at a cross late on that Rolando could only head wide, but healthier as the visiting team were with Rio Ferdinand restored to central defence alongside Nemanja Vidic after a three-match absence through injury, there was only one name on everyone’s lips last night.

If anyone was wondering why Ferguson seems so determined to keep hold of Ronaldo, the United manager need only to point to this game as evidence of the Portuguese’s undoubted worth.

A lot of United fans will tell you that they would be happy to see the back of Ronaldo given his blatant flirtations with Real Madrid and occasionally sickening histrionics on the field, but the question is this: would United have won this game without the Fifa World Player of the Year?

With Dimitar Berbatov again flattering to deceive and Wayne Rooney looking unhappy marooned on the right-hand side, it is doubtful. Fresh speculation about Ronaldo’s future had surfaced before kick-off when Ramón Calderón, the former Real Madrid president, claimed that a world-class player, understood to be Ronaldo, had a formal agreement to join the Spanish champions in the summer, but it is easy to see why Ferguson is prepared to put up with all manner of petulance to keep the forward.

Ronaldo did not have his best game, but his twentieth goal of the season — a remarkable tally given that he has performed with an apparent indifference for much of the campaign — would nonetheless prove decisive, a telling reminder of just what he brings to this United team. It was an absolute peach, too, one that rocked Porto on their heels before United inexplicably decided to sit back and defend a one-goal lead, a surprising decision for a team that had shipped 11 goals in their past five matches.

There was nothing on when Ronaldo collected Anderson’s pass 40 yards from goal, but within seconds, the ball was fizzing its way past Helton into the top left corner to the astonishment of everyone in the ground.

Even by the Portugal forward’s high standards, it was a stupendous strike, one that he celebrated wildly while manhandled by his team-mates. Booed mercilessly throughout by the Porto fans because of his past association with Sporting, this was a classic example of Ronaldo sticking up two fingers to his critics and detractors.

So Ferguson had got his wish “to get into the rhythm of the game quickly”, although thereafter United seemed to be playing a dangerous game of chance. They had started the match in a hugely adventurous 4-2-4 formation, with Ferguson seemingly saying, “To hell with it, go for the jugular”, but such abandon dissipated after the first ten minutes. Instead, with United consumed by caution, Porto were given grounds for encouragement when they should not have been.

Raul Meireles’s free kick from the right was headed only narrowly wide by Bruno Alves, who had also tested Van der Sar with a free kick of his own before then. United should still have been two goals to the good by half-time, though. Ryan Giggs had a neat half-volley spilt then smothered by Helton before the winger flung over a corner a minute before the break that was flicked on by John O’Shea. With the goal gaping from two yards out and only a firm touch needed to steer the ball in, Nemanja Vidic somehow managed to slice his shot on the stretch over the bar. It was an awful miss, one United must have feared might come back to haunt them.

Fortunately for United, the dreaded equaliser, the one that would have sent them tumbling out, never materialised, but when Rolando headed wide after Van der Sar had got his bearings all wrong and Lisandro López sent a scissor kick wide, Ferguson could have been forgiven for wondering if Porto might nick another late goal.

They had done that in the first leg at Old Trafford, after all, and five years earlier when Costinha’s last-minute strike was enough to eliminate United and send a Porto team coached by José Mourinho through, but United had learnt their lesson at the third time of asking. Ferguson will hope it is onwards and upwards from here, even if Wenger might have something to say about that.

Porto (4-3-3): Helton - C Sapunaru (sub: T Costa, 80min), Rolando, B Alves, A Cissokho - L González (sub: Mariano, 32), Fernando, R Meireles - L López, Hulk, C Rodríguez (sub: E Farías, 64). Substitutes not used: Nuno, M Stepanov, F Guarín, A Madrid.

Manchester United (4-2-4): E van der Sar - J O'Shea, R Ferdinand, N Vidic, P Evra - M Carrick, Anderson (sub: P Scholes, 78) - W Rooney, CRonaldo, D Berbatov (sub: Nani, 68) R Giggs. Substitutes not used: B Foster, G Neville, J Evans, CTévez, F Macheda. Booked: Vidic, Evra.

Referee: M Busacca (Switzerland).