MILAN, April 18 (Champions League) - Barcelona are in pole position to qualify for the Champions League final after a second-half strike from Ludovic Giuly gave them victory at the San Siro.
Milan are playing in their third Champions League semi-final in four years and twice went close to opening the scoring through Alberto Gilardino.
But Barca claimed a crucial away goal - and eventually a first-leg advantage - after Ronaldinho prised open the Milan defence in the 57th minute for Giuly, the only Barca player to have played in a Champions League final - with Monaco in 2004.
With so much at stake it was no surprise to see neither side willing to give anything away in the opening stages but the game came to life in the 14th minute following some poor defending by Rafael Marquez.
The Mexican defender failed to deal with a long throw-in from Milan's left and Gilardino slipped between Marquez and Oleguer Presas.
Gilardino was only a few yards out but was at a tight angle and his left-footed effort struck the post and came back into play, with Andriy Shevchenko's 20-yard shot comfortably saved by Victor Valdes.
Then a minute later, Gennaro Gattuso released Clarence Seedorf on the left and the Dutch midfielder crossed for Shevchenko, whose back-post header was turned wide by Valdes.
It took 22 minutes for Barca to test Milan goalkeeper Dida but Samuel Eto'o's low drive was straight at the Brazilian international.
Ronaldinho took time to make his mark and his first effort was a 29th-minute free-kick blocked by the Milan wall, and a minute later, Andres Iniesta's through-ball was just too long for Giuly.
Five minutes later, Carles Puyol was booked for bringing down Kaka although Milan's Brazilian forward looked to have gone down rather easily, and Andrea Pirlo was narrowly wide with the free-kick.
Pirlo was then dispossessed by Giuly and Barca surged forward through Ronaldinho and Eto'o only for Giuly to produce a tame shot at Dida.
The two teams saw out the remainder of the half but six minutes after the restart, Gilardino again came within inches of breaking the deadlock.
Shevchenko superbly chipped the ball over the Barca defence for Kaka, who squared unselfishly for Gilardino but the Italy striker was unable to get enough purchase on the ball and side-footed wide from seven yards.
The breakthrough came six minutes later yet it was the Spanish champions that were celebrating after some sublime play from Ronaldinho.
The Brazilian superstar held off Gattuso before clipping a ball through for Giuly and the Frenchman raced onto the pass before lashing a left-footed volley past Dida from a tight angle.
Gattuso might have drawn level in the 64th minute but his back-post header from Shevchenko's cross managed to go backwards rather then towards goal.
Barca then broke through Ronaldinho, who struck the inside of a post from the edge of the area, while Dida saved well from Iniesta after some good play between the Barca midfield, which had now taken complete control.
However, Kaka finally began to pose the Barca defence some problems, firing wide from distance and then playing a delightful ball for substitute Massimo Ambrosini, who dragged his shot wide from just 14 yards with 10 minutes remaining.
With a minute remaining Kaka jinked into the area but was forced to concede defeat in the creative battle with his international team-mate as his shot flashed narrowly wide.