Luan Oliveira opened the scoring 5:05 into the first quarter and San Diego never looked back.
Erick Tovar added a second less than a minute later but Ontario pulled one back as Jinho Kim stuck home a free kick at the 7:16 mark.
The Southern California rivals clash again on Tuesday at the Citizens Business Bank Arena with kick-off scheduled for 7:05 p.m.
Tovar opened the scoring in the second quarter with the goal of the match. A former MASL winner with Monterrey, the burly striker picked up the ball along the boards and cut inside before unleashing a rocket into the upper corner.
The Mexican then turned provider with a gorgeous ball threaded through to the back post for Brian Farber to tap home.
Leonardo De Oliveira scored with rasping drive when there was seemingly no danger to close the gap to 4-2 at the midway point of the second frame.
Kraig Chiles closed out the first-half by restoring San Diego’s three-goal lead with a half-volley 1:35 before the half-time festivities.
Eduardo Velez scored the only goal of the third quarter as he picked the pocket of an Ontario defender deep in the offensive end. Chiles got on the lose ball and laid if off for “El Vaquero” to sweep the Sockers into a 5-2 lead.
Ray Reza started off a frantic finale with a goal almost eight minutes into the final frame. The 27-year-old flew forward and volleyed off the glass above Ontario goalkeeper Joey Kapinos before deftly heading his own rebound into the far corner.
Andy Reyes and Alex Caceres scored with the sixth attacker to bring some nervous energy into the arena as the gap closed to 7-4, but Oliveira and Farber completed their braces with empty netters to close out the victory.
If Ontario takes game two, the mini-game will take place 15 minutes after the final whistle.
San Diego, however, will be hoping to take care of business in regulation and advance to the Western Conference Finals where Soles de Sonora is waiting in the wings.
You can catch all the Sockers game live on MASLtv YouTube. Make sure to follow San Diego Sockers on social media @sandiegosockers on Facebook, Instagram, Twitter and Snapchat! #Questfor15