Louis Saha's stunning finish gave Manchester United a crucial Champions League win against Benfica in the Stadium of Light.
Saha celebrates his winner against Benfica
Saha struck with a rising angled drive on the hour to give United their first away win in the Champions League for nearly three years.
Benfica dominated the first half, with Nuno Gomes narrowly off target.
But United took control after the goal and Benfica keeper Quim made several fine saves in the closing stages.
The win gave United a measure of revenge for the defeat against Benfica that knocked them out of last season's tournament.
United boss Sir Alex Ferguson sprung a tactical surprise by using Wayne Rooney in a left-flank role, a decision that restricted him to mainly defensive duties in the first 45 minutes and severely limited United's attacking options.
Ronaldo, a target for opposition fans in the Premiership after his role in Rooney's World Cup red card against Portugal, was the villain of the piece again, but on this occasion because of his links with Benfica's fierce rivals Sporting Lisbon.
But he was undeterred and was easily United's most dangerous forward in an opening half dominated by Benfica.
Michael Carrick and Paul Scholes picked up bookings for fouls inside the first 10 minutes, but United could also have taken the lead early on when Ronaldo's shot on the turn was fumbled by Benfica keeper Quim, and Saha was just unable to turn in the rebound.
Benfica, however, made most of the running, with Giorgios Karagounis forcing a fine save from Edwin van der Sar and Nuno Gomes shooting inches wide after Nemanja Vidic conceded possession in a dangerous position.
United desperately needed a moment of inspiration and Saha provided it, against the run of play, on the hour.
Ronaldo found the France striker on the right flank, and he cut inside to deliver a venomous left-foot drive that flashed past Quim via a slight deflection off Anderson.
Rooney had been a peripheral figure but he had a chance to score his first Champions League goal for two years as he broke clear, only to send a tame finish straight at Quim.
United had looked far more composed in possession since the goal while Benfica, in contrast, looked drained of the confidence that had characterised their performance in the first half.
Saha could have sealed the win with 14 minutes left when he stole in at the near post to meet Carrick's cross, but he shot just inches wide.
Ferguson made a double substitution to protect United's lead, sending on Darren Fletcher and Alan Smith - his first senior appearance since breaking his leg at Liverpool seven months ago - for Rooney and Saha.
Quim then made a brilliant triple stop after 87 minutes as United closed in on victory.
He dived to stop Gabriel Heinze's free-kick and recovered to make quick-fire stops from Fletcher and Carrick.
Benfica: Quim, Alcides, Luisao, Anderson (Mantorras 82), Leo, Petit, Katsouranis, Karagounis (Nuno Assis 62), Paulo Jorge (Miccoli 65), Nuno Gomes, Simao.
Subs Not Used: Moretto, Beto, Nelson, Ricardo Rocha.
Booked: Katsouranis, Petit.
Man Utd: Van der Sar, Neville, Ferdinand, Vidic, Heinze, Ronaldo, Carrick, O'Shea, Scholes, Rooney (Fletcher 86), Saha (Smith 85).
Subs Not Used: Kuszczak, Evra, Brown, Solskjaer, Richardson.
Booked: Carrick, Scholes, Heinze.
Goals: Saha 60.
Ref: Frank De Bleeckere (Belgium).