Champions League - Giggs rescues point for United
Oscar Cardozo's brilliant first-half effort had given the Portuguese side a deserved lead in Lisbon but Giggs hit back with an equally impressive strike just before half-time.
Giggs's goal - which extended his own record as the oldest scorer in the Champions League - was the undoubted highlight of an otherwise lacklustre performance from the Premier League champions, although points dropped at Benfica in a group also containing FC Basel and Otelul Galati should not give Alex Ferguson too many sleepless nights.
Ferguson made eight changes to the team that thumped Bolton 5-0 in the Premier League at the weekend as the United manager opted against sending out the new-look team that has so impressed this season and instead reverted back to an XI far more resembling the one which reached last year's final.
Seven players who started that game at Wembley took to the field in Lisbon, as Antonio Valencia and Darren Fletcher returned from injury and illness to make their first starts of the season. Goalkeeper Anders Lindegaard was also brought in, with summer signing David De Gea taking his place on strong bench alongside Michael Owen, Anderson, Dimitar Berbatov, Javier Hernandez, Nani.
Yet the changes in personnel did little for the Premier League champions and they started the game without the fluency to their play that has so far this season been their calling card.
Nicolas Gaitan flashed a shot across Lindegaard's goal and the Dane was brought into action by Cardozo before the Paraguayan striker opened the scoring with a sumptuous piece of individual skill in the 24th minute.
Cardozo took down a long ball forward on his chest before turning the leaden-footed Evans in one swift movement and firing low past Lindegaard. It was the first time United had conceded on their travels in the competition since a quarter-final against Bayern Munuch two seasons ago, but it was nothing less than the home side deserved.
Evans continued to look shaky on occasion as Benfica threatened to add to their lead as the half progressed but United clawed their way back onto level terms, totally out of blue, thanks to Giggs just before the break.
The veteran midfielder, otherwise rather ineffectual in the hole behind Rooney, seared in from the right before lashing a left-footed drive into the top corner from the edge of the penalty area. At the age of 37 years and 289 days he is the oldest player to have scored in the competition and the goal also saw him overtake Raul as the player to have scored in the most Champions League seasons - 16 in all.
He could have added to his tally on 63 minutes following some neat footwork to fashion a shooting chance but his clipped effort was diverted around the post by Artur.
At the other end, Lindegaard was also in action after the break, the Dane producing crucial stops to deny Nolito and then the impressive Nicolas Gaitin.
In between those chances, Emerson nearly capped a fine one-two with Nolito with a shot on target - he could only fire into the side netting - and with three minutes remaining on the clock, Nolito prodded into the side netting when perhaps he should have done better.
United, meanwhile, failed to produce much of note at the other end and will perhaps feel fortunate to escape with a point after what was an under-par performance, given the sky-high standards they have set for themselves so far this season.