The Colorado Rapids began their title defence with a 3-1 Major League Soccer victory over the Portland Timbers on Saturday.
First-half goals from Jeff Larentowitcz, Omar Cummings and Jamie Smith put the MLS Cup champions in control before Kenny Cooper pulled a goal back for the visitors 11 minutes from time.
DC United kicked off their campaign with a 3-1 triumph over the Columbus Crew.
Substitute Charlie Davies scored twice - the first from the penalty spot - to stretch the lead given to United by Josh Wolff six minutes after the break. Another substitute, Robbie Rogers, reduced the deficit for Columbus 12 minutes from time but they could not find a way back into the match.
FC Dallas earned a 1-1 home draw against the Chicago Fire despite playing for more than half an hour with only 10 men.
MLS debutant Diego Chaves' 17th-minute strike put the Fire ahead but Milton Rodriguez restored parity just 60 seconds later. Dallas had Brek Shea dismissed 10 minutes after the interval but there were no further goals.
Omar Bravo scored twice to help Sporting Kansas City to a 3-2 win at Chivas USA. CJ Sapong put the visitors ahead in the second minute and Bravo netted on the stroke of half-time to double their advantage.
Jimmy Conrad got the hosts back in it 11 minutes after the interval but Bravo's second goal in the 74th minute restored Kansas' two-goal cushion before Ben Zemanski's late consolation.
The Seattle Sounders suffered their second straight loss, Juan Agudelo's first MLS goal lifting the New York Red Bulls to a 1-0 win.
The Vancouver Whitecaps were 4-2 winners against Toronto FC. Goals from Eric Hassli and Terry Dunfield - either side of Dwayne De Rosario's equaliser - gave the Whitecaps a half-time lead and further efforts from Atiba Harris and Hassli again made the result safe before Maicon Correa pulled one back for Toronto.
Danny Califf's fifth-minute strike was enough to clinch the Philadelphia Union a 1-0 win at the Houston Dynamo, while Kyle Beckerman's second-half goal secured Real Salt Lake a 1-0 victory at the San Jose Earthquakes.