The Major League Soccer side even looked good for about 18 minutes with Beckham, who starred for the Red Devils in his prime, having a great chance in the seventh minute, only to see his 25-yard strike slide wide of the goal.
Rooney though gave the Manchester United faithful in the mixed crowd "half for United, half for the MLS squad" something to cheer about in the 20th minute.
"They are so quick to the ball, and it's one or two touches and they are going and they are not letting up," MLS defender Tim Ream said. "With Rooney, that just shows how much of a well-rounded player he is."
Rooney made a pass to Berbatov at the top of the box, took a return pass and then found Anderson breaking into the area alone for a wide-open shot that easily beat goalkeeper Faryd Mondragon.
"I had no chance," Mondragon said. "It was like a penalty kick."
Beckham had a chance to equalize two minutes later, but United keeper Ander Lindegaard parried his 20-yard blast over the crossbar.
Park broke the game open in the 45th minute when he took a pass from Patrice Evra at the top of the box, got around defender Sean Franklin and then launched a left-footed shot into the top right corner of the net.
"To be honest I was more disappointed with the second goal because I got a piece of that," Mondragon said. "But it was a great goal."
Rooney helped stretch the lead to 3-0 in the 52nd minute, looping a pass over the defense to Berbatov. The Bulgarian chipped the ball over rushing backup goalkeeper Tally Hall, only to see it hit the crossbar. Berbatov chested down the rebound and ripped a shot into the net.
Welbeck closed out the scoring in the 68th minute with a shot from the top of the box that deflected off defender Geoff Cameron past Hall.
AP