Manchester United were indebted to a superb Ryan Giggs goal as they drew 1-1 with Benfica on Wednesday despite a below-par performance in their Champions League Group C opener.

Giggs, 37, sent a rocket into the top corner three minutes before half-time to cancel out Oscar Cardozo's 24th-minute opener for a Benfica side who seemed intent on puncturing their opponents' early-season momentum.

At Lisbon's iconic Estadio da Luz, United looked a shadow of the side that has soared to the top of the Premier League with 18 goals in their first four games.

It was only thanks to Giggs and some fine goalkeeping from competition debutant Anders Lindegaard that Sir Alex Ferguson's decision to rest a string of players did not backfire.

"Once we scored, we played well," said the United manager.

"Our possession was too cautious in the first half. It was the kind of possession that gives you a certain control but doesn't win you the game.

"Benfica had some terrific chances in the last 15 minutes. There was one very good chance, and Anders made a great save."

In all Ferguson made eight changes to the side that beat Bolton 5-0 on Saturday, in a nod to Sunday's visit of Chelsea.

Patrice Evra, Jonny Evans and Wayne Rooney were the only men to keep their places.

Mindful, perhaps, of United's pedigree, Benfica were initially content to concede the initiative but uncertainty in the visitors' play allowed Jorge Jesus' men to assert themselves.

"We had more chances than them," said the Benfica coach. "I think the result was fair, but we played very well. It would have been great to beat such a great team as Manchester, but the point is important."

Cardozo registered Benfica's first shot on target with a low effort that Lindegaard claimed comfortably but the Paraguayan was less merciful in the 24th minute.

Collecting a high pass from the enterprising Nicolas Gaitan on his chest, he turned Evans adroitly before clipping an accomplished finish inside Lindegaard's right-hand post.

It was the first away goal United had conceded in the competition since their quarter-final loss to Bayern Munich in the 2009-10 tournament.

United's only effort of note had been a shot from a tight angle that Antonio Valencia blazed over the bar, but from nowhere Giggs rolled back the years to produce a stunning equaliser that silenced the home fans.

After picking up possession on the right-hand side, the Welshman spied a pocket of space on the edge of the box that he surged into before arrowing a fine drive into the top-right corner.

Giggs' goal, from United's first shot on target, broke his own record for the tournament's oldest goalscorer and means he has now scored in more Champions League campaigns -- 16 -- than any player in history.

His intervention could not disguise United's problems, however, and Benfica continued to look dangerous in the second half.

Pablo Aimar fizzed a low effort narrowly wide and although Giggs drew a save from Artur after wriggling into the area, Lindegaard then had to produce a brilliant stop to palm away a side-footed effort from substitute Nolito.

When Emerson advanced from left-back and toed a shot across goal, Ferguson decided he had seen enough and sent on Nani and Javier Hernandez in place of Darren Fletcher and Valencia.

There was no stemming the red Benfica tide though and after Lindegaard had pushed away a curler from Gaitan, Phil Jones was sent on to add muscle to the creaking away defence.

A late let-off for United saw Nolito find the side netting from close range with three minutes left and Ferguson will ultimately have been thankful that his side's most challenging fixture of the group phase did not prove more costly.