The Quakes beat the reigning MLS Cup champions courtesy of Chris Wondolowski's 30th-minute opener before Amarikwa added a second with a spectacular chipped effort from more than 30 yards.
Jack McInerney pulled one back for the Timbers but it was Amarikwa's moment of brilliance which had done the damage for the Californian club.
After the match, the 28-year-old forward spoke of his sublime effort which he says was sparked by watching Golden State Warriors superstar Steph Curry drain continuous three-pointers in the NBA this season.
“Most goalkeepers play off their line, so I thought if I can turn quickly I have an opportunity," he said.
“When I took my first touch long, the keeper was off of his line unsure if he should come or not. Then on my second touch, I looked up and figured if I put it over his right and he would have difficulty getting to it.
“Once I made contact with it, I knew I hit how I wanted to. Luckily, it fell in the back of the net."
He added: "I've been watching Steph Curry shoot from everywhere. If he can do it I can get lucky one time."
Check out the cracking goal below: