(CNN) -- Cristiano Ronaldo missed an early penalty as Manchester United earned a 0-0 draw in the first leg of the Champions League semifinal at Barcelona's Nou Camp stadium on Wednesday night.



Cristiano Ronaldo sent his penalty attempt wide as United failed to take an early lead at the Nou Camp.



The Portugal winger, the top scorer in this season's competition, spurned the chance to net for the 39th time overall this campaign and give United a vital away goal.



The 23-year-old hit the stanchion high outside goalkeeper Victor Valdes' left-hand post in the third minute after Gabriel Milito handled his header from a Paul Scholes corner.



It was United's best chance in a game dominated by the home side, who had the best of possession with some silky moves but failed to find the killer pass in the final third of the pitch.



United goalkeeper Edwin van der Sar made a string of saves, especially in the second half, but was not often seriously tested.



Barcelona were boosted by the return of Argentina forward Lionel Messi, who started alongside Samuel Eto'o up front, with Thierry Henry on the bench after also being cleared following an illness.



Messi picked out Samuel Eto'o in the 13th minute only for midfielder Scholes -- making his 100th Champions League appearance -- to make a vital interception.



Barcelona pressed forward again in the 21st minute and Rafael Marquez got clear of his marker but his header failed to trouble Van der Sar, who was back in the side following a groin injury.



Then Yaya Toure showed good skill for the home side and sent a good cross into the area that was turned away by Van der Sar.



Ronaldo felt he should have had another penalty in the 30th minute when he was bundled over by Marquez after Xavi had carelessly lost possession, but Swiss referee Massimo Busacca allowed play to continue.



Eto'o rattled in a shot after 34 minutes but Wes Brown -- who passed a late fitness test to replace the ill Nemanja Vidic in central defense -- made a vital block.



Brown partnered Rio Ferdinand, with England midfielder Owen Hargreaves operating as a makeshift right-back.



Deco, starting his first game for Barcelona after two months out with injuries, then failed to test Van der Sar with a free-kick in the 38th minute.



Marquez was booked in the 44th minute after tripping Ronaldo as he attempted to surge forward, meaning the Mexican is suspended for next Tuesday's second leg at Old Trafford.



Ronaldo sent his effort from an acute angle wide of the post.



After the break, Messi saw his effort blocked in the 47th minute and then Van der Sar tipped over defender Gianluca Zambrotta's long-range effort.



Messi beat three United players but Ferdinand cut out his low cross from the right, then he played in a superb ball for Eto'o -- who lashed his shot against the side-netting.



Deco tested Van der Sar with a low drive, then the Dutchman easily dealt with a 20-yard effort from Xavi.



Barcelona coach Frank Rijkaard took off Messi in the 62nd minute, replacing him with teenager Bojan Krkic, who scored the winner in the first leg of the quarterfinal against Schalke.



A foul on the Serbian-born Spaniard drew a yellow card for Hargreaves in the 73rd minute, then United boss Alex Ferguson bolstered his midfield by bringing on Nani for England forward Wayne Rooney -- who had started up front with Carlos Tevez.



Rijkaard responded by replacing Deco with Henry in the 77th minute, and the French forward forced a scrambled save by Van der Sar with a long-range shot on 83.



Ferguson brought on veteran winger Ryan Giggs for Tevez soon after, then Van der Sar denied Andres Iniesta and also dived to comfortably save Henry's free-kick from 35 yards.



Barcelona continued to press until the final whistle, but still could not create a clear-cut opportunity. E-mail to a friend
Who dominated the Champions League? What happens to Cristiano Ronaldo in the third minute? Did the Goalkeeper make many saves? Which teams had a draw? What is the Goalkeeper's name? What was the score on the fist leg of the semifinals? What is the name of United's top scorer?
Barcelona The 23-year-old hit the stanchion high outside goalkeeper Victor Valdes' left-hand post in the made a string of Manchester United Victor Valdes' 0-0 draw Cristiano Ronaldo
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