A crowd of 52,342, the biggest for Manchester United on its North American tour so far — eclipsed the 37,319 who witnessed a World Cup qualifier here in 2001.
The crowd may have also been drawn partly out of curiosity to see the newly renovated Arrowhead Stadium, which was hosting its first event after a $325 million makeover.
Backup goalkeeper Eric Kronberg replaced Jimmy Nielsen at halftime and made five saves for the Wizards, who have not won an MLS title since 2000 and are 4-8-4 this season.
In the 11th minute, Arnaud beat United's offside trap and took a well-placed through ball from Kei Kamara. Given the one-on-one against backup keeper Ben Amos, Arnaud dribbled into the penalty area and calmly slotted the ball into the lower left corner.
Dimitar Berbatov equalized from the penalty spot in the 41st minute after defender Jimmy Conrad was sent off for a sliding tackle on him.
Replays appeared to show Conrad made contact with the ball before Berbatov went down, but referee Terry Vaughn went straight for the red card and Berbatov converted with a roller into the lower right corner.
Kamara's goal put the Wizards up 2-1 in the 42nd minute. He headed Ryan Smith's corner kick over Amos and off the underside of the crossbar, and the ball landed just over the goal line.
Manchester United, the world's biggest soccer brand and a longtime power in the English Premier League, played without several of its stars, including Ji-Sung Park, Rio Ferndinand, Wayne Rooney and Michael Carrick.
The Wizards had 12 shots in the first half to five for the Red Devils, and led on shots on goal 6-4.
Manchester United's next stop will be a match against the MLS all-stars on Wednesday in Houston.
Earlier Sunday, the New York Red Bulls beat Manchester City, another English Premier League heavyweight, 2-1.
Officials hoped a big, enthusiastic crowd would help the town's bid to host future World Cup games.
"I'm very optimistic that the United States has a very good shot at landing the 2022 World Cup, and Arrowhead is on the list as one of the 18 stadiums that would be a possible venue for that game." Hunt lobbied hard to get the Manchester United-Wizards match.
"Events like tonight's where we're going to have over 50,000 people in the building for a soccer game I think will be a big selling point for both FIFA and U.S. Soccer when it comes time to make the decision on which stadium to bring the World Cup to," he said.