-LRB- CNN -RRB- -- 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