United (14-8-4) extended its lead to four points over second-place Sporting Kansas City in the Eastern Conference.
Four-time champion Bayern Munich, Manchester City and CSKA Moscow — who also faced each other last season — are joined by Roma in perhaps the toughest group.
Taking over the leadership of an inexperienced squad that is recovering from the national team’s worst-ever World Cup, Rooney knows the rebuilding process requires unity.
The 32-year-old Alonso has been with Real Madrid since 2009 and won the Champions League with the club in May. Madrid knocked out title holder Bayern in the semifinals.
Los Angeles (12-5-7) won its third straight game for the first time this season, while D.C. United (13-8-4) lost for the first time in three matches.
The 26-year-old Di Maria joined on a five-year contract, taking United’s spending to about 130 million pounds ($215 million) in the summer transfer window as England’s most successful club seeks to revive its fortunes under new manager Louis van Gaal.
Since making his England debut in 1999, the 36-year-old Lampard has scored 29 goals in 106 matches, with his last appearance coming at the World Cup in June.
Nineteen months after ending a 2½-year spell with Manchester City to play for his boyhood club, Balotelli returns to the English Premier League as a replacement for Luis Suarez — another of world football’s talented but disruptive stars.
Fabian Espindola scored in the 24th minute, Chris Rolfe in the 28th and Perry Kitchen in the 31st to move United (13-7-4) one point ahead of Sporting KC (12-7-6) into the conference top spot.
The three-time World Cup veteran has asked U.S. coach Jurgen Klinsmann not to consider him for selection to the roster until September 2015. Howard is not retiring from international play, however; the decision is driven mainly by his desire to spend more time with his family.
United (12-7-4) opened the scoring in the 11th minute. Taylor Kemp sent a perfect through-ball to Silva, who faked Drew Moor to the ground and chipped his shot over Clint Irwin for the early lead.
Louis van Gaal failed to usher in the bright new era expected at United on Saturday, watching in frustration as the team opened the season with a home loss for the first time in 42 years.