Gonzalo Martinez came off the bench to break the deadlock in the 89th minute before Josef Martinez sealed Atlanta United's victory.
New York Red Bulls claimed a derby win over New York City, thanks to a Daniel Royer brace.
LAFC maintained their commanding lead in the race for the Supporters' Shield at Banc of California Stadium on Saturday.
LAFC continued their fine form by blitzing Sporting KC as Chicago Fire capitalised on their numerical advantage against Atlanta United.
The San Jose Earthquakes recorded a 3-0 win over LA Galaxy in the California Clasico.
Zlatan Ibrahimovic and Wayne Rooney are the big-name omissions from the Opta-powered MLS mid-season Team of the Year.
Saphir Taider's brace guided Montreal Impact to a hard-fought MLS win over Seattle Sounders.
LAFC crashed the re-opening of Portland's Providence Park on Saturday – star Carlos Vela scoring again to lead the visitors.
Chris Wondolowski broke Landon Donovan's record with four goals in last week's victory and the veteran was at it again on Sunday.
DC United were beaten in MLS on a day that belonged to San Jose Earthquakes forward Chris Wondolowski.