Palace did well to resist United in the first 45 and even enjoyed more of the possession in an underwhelming first-half for the champions.
The closest effort for the visitors came when Marouane Fellaini’s left-footed effort from inside the box went high and wide.
But Marouane Chamakh gifted the Red Devils a golden opportunity take the lead on the hour mark.
The drifting Palace forward was penalised for taking out left-back Patrice Evra with a clumsy challenge just inside the box.
Referee Michael Oliver pointed to the spot for Robin van Persie to convert expertly by sending ‘keeper Julian Speroni the wrong way.
The game was wrapped up four minutes later when Wayne Rooney, who yesterday signed a £300,000 contract deal at Old Trafford, volleyed into the top corner.