Leader of the Western Conference, Los Angeles recorded a resounding 5-0 victory over San Jose Earthquakes.
Vela opened the scoring in the eighth minute when San Jose goalkeeper Daniel Vega missed his clearance from a Mark-Anthony Kaye pass, allowing the Mexican to tap in.
A beautiful pass from Eduard Atuesta set up Steven Beitashour for LA's second before Vela scored again on the stroke of half-time after a pass from Diego Rossi.
Vela completed his hat-trick in stunning fashion, curling a wonderful 25-yard effort into the top corner, before he also set up Rossi.
That proved not to be the biggest win of the day as Sporting hammered Montreal Impact 7-1.
Johnny Russell scored a fine opener before Gerso Fernandes set up Nemeth in the 43rd minute.
Gerso also set up Felipe Gutierrez prior to the break, and it got ugly for Montreal in the second half.
Russell completed his brace before setting up Nemeth, who had a hat-trick after Gianluca Busio also got on the scoresheet.
Saphir Taider managed a late consolation goal for Montreal.
Elsewhere, Atlanta United's winless start to the season continued with a 2-0 loss to Eastern Conference leader Columbus Crew.
Chicago Fire edged New York Red Bulls 1-0 and New England Revolution overcame Minnesota United 2-1.
Philadelphia Union recorded a 2-0 win over Cincinnati, Houston Dynamo cruised past Colorado Rapids 4-1, Dallas beat Real Salt Lake 4-2 and Vancouver Whitecaps and Seattle Sounders drew 0-0.