A brilliantly struck but controversially awarded goal by Roberto Carlos earned Real Madrid a 2-1 victory over Juventus in a tense Champions League semi-final first leg on Tuesday.

Real, looking to take a step closer to what would be a 10th European Cup win, moved ahead after 23 minutes at a rain-swept Bernabeu when the ball broke to Ronaldo outside the area and the Brazilian tucked a shot past Gianluigi Buffon.

Juventus poached an equaliser through David Trezeguet just before halftime and the Italians took command after the break.

The tide turned on 73 minutes when Roberto Carlos let fly from outside the area with a left-foot thunderbolt.

At least three Real Madrid players were in offside positions, possibly blocking the view of Buffon, but after consulting with his linesman, referee Terje Hauge ruled the goal as valid.

Real might have added to their lead, with Luis Figo forcing a classy save from Buffon in the 90th minute and Ivan Helguera just failing to turn in a Roberto Carlos cross seconds later.

The result gives Real a slim advantage to take to Turin for the second leg but with an away goal Juventus are still very much in the hunt for a place in the final against either AC Milan or Inter Milan in Manchester on May 28.

Real and Juventus were meeting for the first time since the Spanish club's victory in the Champions League final in 1998 -- the first of three European Cup wins in five seasons for Real.

Zinedine Zidane was a Juventus player on that occasion but now in the white of Madrid, the French midfielder was for long periods the main obstacle blocking his former club's hopes of revenge.

Zidane was outstanding throughout, keeping the Juve defence on guard with a series of quick passes out to Figo on the right and Roberto Carlos on the left and tackling back to limit the influence of his Czech replacement Pavel Nedved.

Zidane came close to opening the scoring on 15 minutes when his curling free kick was nervously pushed away by Buffon.

The goal was not long coming, as the ball broke to Ronaldo after Mark Iuliano tackled Fernando Morientes on the edge of the box.

The Brazilian striker immediately pounced to side-foot the ball in at Buffon's near post.

Fernando Morientes missed a great chance to put the reigning European champions two up when he was put through by Ronaldo on 44 minutes only to blast his shot over the bar.

A few seconds later, Juventus were level. Alessandro Del Piero collected a high ball from the right and took a shot that deflected off Michel Salgado and straight to Trezeguet, who gratefully bundled it in.

Ronaldo was forced off through injury shortly after the break and with Raul missing after his recent appendix surgery the home side was short of their usual finesse in attack.

Morientes forced a good save on 70 minutes and seconds later Roberto Carlos thudded a shot across the face of goal, with substitute striker Javier Portillo only just failing to get a touch at the far post.

Roberto Carlos was more accurate in Real's next attack as he restored the team's lead with his superb strike.