The Portuguese winger stepped up to convert a 44th-minute penalty after Michael Carrick was fouled by Mikel Arteta to take his tally to 13 league goals.

United should have been awarded another penalty shortly after the restart when Carrick was once again brought down inside the area, this time by Joleon Lescott, but the referee waved play on.

The Red Devils recorded their 12th consecutive clean sheet to demonstrate their defensive solidity that is orchestrated by the evergreen Nemanja Vidic.

United, who are looking to win a third successive league title, are on top of the table with 53 points.

Chelsea and Liverpool, who both have 48 points, meet on Sunday with the hope of narrowing the gap with Alex Ferguson's team.