Danny Welbeck opened the scoring with an away goal for Sir Alex Ferguson's side before the former Old Trafford star equalised with a bullet header past the impressive David de Gea
Danny Welbeck opened the scoring for the Premier League leaders with a 20th minute header to deliver United a crucial away goal.
Ten minutes later, Ronaldo made sure of the headlines as he equalised with a header of his own to score his 37th goal of the season and set up a finely balanced second leg when Madrid travel to Old Trafford on March 5.
Ronaldo was low-key in his celebrations as he came up against United for the first time since leaving for Madrid in a world record £80 million deal in 2009, but he could not find a second goal as the Spanish giants’ prospects of a landmark tenth European title were dented.
Robin van Persie almost made it a perfect night for Sir Alex Ferguson’s side 18 minutes from time but was denied twice in matter of seconds - first by the crossbar and then Xabi Alonso’s goalline clearance.
As these two heavyweights went head-to-head in the tie of the round, this end-to-end game delivered on the palpable pre-match expectation - with neither side able to deliver an early knock out blow.
United, though, will be the happier of the two sides, with Ferguson rewarded for the bravery of his attacking line-up, even if he may want to share his post-match bottle of wine with his goalkeeper David De Gea, who made a series of fine saves to keep Madrid at bay.
There was a carnival atmosphere in the Spanish capital throughout the day as thousands of United fans soaked up the atmosphere with lager and tapas in the city’s squares, pubs and bars.
The anticipation was reflected inside the Bernabeu, where the teams were greeted by a wall of noise as the Madrid fans unfurled banners and flags, while their United counterparts sang their hearts out high in the Madrid sky.
United boss Sir Alex Ferguson made his intentions clear by fielding an attacking quartet of Van Persie, Welbeck, Wayne Rooney and Shinji Kagawa while captain Nemanja Vidic was rested from the squad entirely as he recovers from a knee injury.
Real Madrid sprung no surprises in their starting line-up, with French defender Raphael Varane replacing Pepe at centre-back and Mourinho picking his first-choice midfield and attack.
Both managers spoke before kick-off about the attacking traditions of their clubs and sent their players on to the pitch to put on a show, with the attacking freedom - and suspect defending - evident in a breathless first half.
Fabio Coentrao almost put the hosts ahead after just five minutes but his right-footed shot from 16 yards was wonderfully tipped on to the far post by United goalkeeper David De Gea with the merest fingertip.
United are no strangers to the big occasion and after settling in to the game, they took the lead with their first real opportunity of the game in the 20th minute with the easiest of goals as they took advantage of Real’s fragility from set-pieces.
Rooney whipped in a corner from the left and as the home defenders stood and watched each other, Welbeck rose to head into the bottom corner to send the 4,000 United supporters into delirium.
Yet Real Madrid responded and put United on the back foot as Ronaldo and Mezut Ozil in particular caused the visitors problems with their movement in the final third.
On the half-hour mark, Ronaldo levelled the scoreline with a trademark header. Di Maria played in an inviting cross from the left and the Portuguese rose high, craned his neck and headed the ball into the corner.
Both teams continued to search for a second goal, Welbeck flicking an inventive effort just wide from a Van Persie cross before Ozil forced De Gea into a sharp save after collecting a raking 60-yard pass by Xabi Alonso.
The action continued after the break, with Di Maria firing just wide before referee Felix Brych infuriated the United bench by waving away appeals for a foul by Varane on Patrice Evra when the United captain would have been through on goal.
On the hour mark, De Gea again denied Madrid the lead, producing an unorthodox save with his feet to kick away Coentrao’s volley when United right-back Rafael again fell asleep defensively.
At the other end, van Persie went agonisingly close for United twice in the space of a minute, first seeing his cracking right-footed shot cannon off the crossbar via the faintest glove from Diego Lopez, then the Dutchman’s scuffed volley beat the Madrid goalkeeper but was cleared off the line by Alonso as it trickled towards the net.
There was still time for Ronaldo to fizz a trademark free-kick just over the crossbar from 35 yards but United held on for a result that surely leaves them favourites to progress to the quarter-finals.