Anderson, Dimitar Berbatov and Danny Welbeck also scored for the reigning English Premier League champions, who have outscored their opponents 18-2 to win the opening four games on their U S tour.
"I liked the result," manager Alex Ferguson said.
Ferguson's side will wrap up its preseason tour in Washington on Saturday against Barcelona in a rematch of the Champions League final which the Spanish team won 3-1. Then it's back to England for the Community Shield game and the start of another season the following week.
The final score might have been a little misleading because David Beckham and his MLS teammates had a couple of good shots at goal, but make no mistake Manchester United was far superior in the game at Red Bull Arena that drew a sellout crowd of 26,760.
The Reds didn't have a lot of chances against the MLS, but when they did they were lethal, especially with Rooney setting up the goals.
In the United States, football fans have seen Rooney scoring again and again in replays of his bicycle kick in a match last season. This time, he was perfect with his passing.
"He's a good passer of the ball," Ferguson said. Like most midseason classics, this one started with a show. Parachutists floated into the double-decked arena that is in its second year of operation, fireworks lit the sky and a helicopter flyover all preceded the start of the game.
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.