Goalkeeper Bill Hamid made two stops to earn his third straight shutout as D.C. United is the lone team to have not allowed a goal this season.
Rooney scored on a penalty kick in the 34th minute and then added another with a chip shot over the goalkeeper in the 41st minute. He completed the hat trick with a perfectly-timed sliding score at the 65th minute of the second half.
Elsewhere, Uruguay international Nicolas Lodeiro set up one goal and scored an audacious penalty as the Seattle Sounders maintained their 100 percent start to the season with a 4-2 victory at Chicago Fire.
The Sounders made it three wins out of three after taking control of the game with two unanswered goals in the opening 15 minutes at Chicago’s SeatGeek Stadium.
Former England star Wayne Rooney scored three goals on Saturday night to lead D.C. United to a crushing 5-0 victory over Real Salt Lake.
Rooney registered his first three goals of the new season and also his first hat trick since signing on with Major League Soccer in July 2018. He now has five multi-goal games.
Lucas Rodriguez and Ulises Segura also scored for host D.C. United, who peppered the Salt Lake goal with 22 shots.
Spanish winger Victor Rodriguez fired Seattle into the lead after eight minutes, tucking away a low finish at the far post after good work down the right by Jordan Morris.
Lodeiro then created Seattle’s second, splitting open Chicago’s defence with a sublime pass to Morris.
The US international striker still had plenty to do, but adjusted his body position brilliantly to steer a finish beyond Chicago goalkeeper David Ousted to make it 2-0.
Minnesota, who have also taken maximum points from their opening two games, can draw level later Saturday with a win over the Los Angeles Galaxy.
Los Angeles FC, the only other team to make a perfect start to the season, face New York City FC on Sunday.
Seattle extended their lead early in the second half when Rodriguez was bundled over in the area on 49 minutes, allowing Lodeiro to step up and chip a Panenka penalty in off the underside of the bar.
Chicago hit back with goals from Raheem Edwards and Fabian Herbers but Raul Ruidiaz’s late goal made the game safe for Seattle, who now lead the Western Conference standings with a maximum of nine points.