The win was Portland's first on its home field in nine games, a stretch that includes five Major League Soccer and four exhibition matches. The last time the Timbers won at Jeld-Wen Field was May 21 against Columbus.
The Timbers (6-10-3 MLS) are 1-3 in exhibition matches this season.
Independiente, of the Argentine Primera Division, has won 16 international championships during its existence and is considered one of the world's most successful club teams.
Coming off a 1-0 loss at Columbus last Saturday, most of the Timbers' starters rested against the Argentina opponent.
Nonetheless, Portland dominated the first half, as the Timbers produced a number of quality scoring opportunities, two that led to goals.
Portland took a 1-0 lead during the 36th minute when Zizzo streaked down the right side of the field and kicked a 15-yard shot past Independiente goalie Hilario Navarro.
Three minutes later, the Timbers struck with a beautiful goal off a set play 35 yards from the goal. Mike Chabala crossed the ball just inside the top of the penalty box, where Umony sent a header over Navarro and into the goal for a 2-0 Portland lead.
Independiente threatened to score a couple of times during the second half. CAI's best chance came during the 85th minute on a set play just outside the penalty box, but Julian Velaquez's kick was turned away by Portland's defensive wall.
Missing from the Timbers was midfielder Jack Jewsbury, who will participate Wednesday night for the Major League Soccer All-Star team against Manchester United in New Jersey.
Portland resumes MLS play Saturday with a home match against Toronto FC.