Uruguay's Vinas scored in the first half and added a second from the penalty spot in the second at Azteca Stadium in rainy Mexico City, where Leonardo Suarez capped the scoring for the Liga MX side after Diego Valeri pulled the Timbers within one with a penalty.
After a 1-1 draw in Portland last week, Club America advanced with a 4-2 aggregate to face the Philadelphia Union, the lone MLS side left standing after Liga MX club Monterrey ousted MLS Cup champions Columbus Crew earlier Wednesday.
Maximiliano Meza's first-half brace propelled Monterrey to a 3-0 victory that saw them advance 5-2 on aggregate to a last-four clash with Cruz Azul.
Cruz Azul had eliminated MLS's Toronto FC on Tuesday, when Philadelphia beat MLS rivals Atlanta to punch their semi-final ticket in CONCACAF's most important competition for clubs from North and Central America and the Caribbean.
The winners of the tournament advance to the FIFA Club World Cup.
Vinas headed America in front in the 21st minute, then saw a 28th minute attempt sail over the crossbar.
Down 1-0 at halftime and having barely tested America goalkeeper Guillermo Ochoa, the Timbers forced him into three saves in the opening minutes of the second half.
But it was the hosts who took a 2-0 lead in the 59th minute, the referee awarding a penalty after Suarez came down in the area after tangling with Claudio Bravo.
Portland keeper Jeffrey Attinella guessed correctly, but his dive to his right wasn't enough to stop Vinas's low effort.
Minutes later, Ochoa stopped a close-range shot by Felipe Mora, but the Chilean attacker came down in the area and this time it was Portland awarded a penalty that Diego Valeri smoothly converted to make it 2-1 in the 64th.
Argentina's Suarez restored America's two-goal lead in the 70th with a blast from outside the box that found its way in at the base of the left post.
In Monterrey, former Independiente striker Meza got the hosts off to a quick start with a goal in the third minute and added a second in the 26th before Miguel Layun capped the scoring the 71st minute.
The Crew, who were without star playmaker Lucas Zelarayan of Argentina because of yellow card accumulation, were overcome early by the drive of Javier Aguirre's men -- who were coming off a 2-2 draw in the first leg in Columbus.
- 'Mountain to climb' -
Meza quickly put Monterrey in the ascendance as he capitalized on an error from the Crew's Dutch goalkeeper Eloy Room.
Monterrey's Vincent Janssen fired a fierce low cross that Room dived to clear from the goal mouth, but sent the ball straight to Meza who fired home from close range.
"Huge mountain to climb when you give up an early goal like that," Crew manager CalebÂ Porter said. "Not the way you want to start the match."
In the 26th minute, Janssen got the better of the Crew's Josh Williams and found Meza, whose right-footed shot saw the Rayados take a 2-0 lead into halftime.
Veteran Mexico defender Layun sealed matters in the 71st with a spectacular free kick over the wall and into the top corner of the net.
The three Mexican semi-finalists are looking to extend the country's long reign of dominance in the event, having won the tournament for the past 15 years running.
The last MLS side to lift the title was Los Angeles Galaxy in 2000.
Standout matches today