The home side pressed forward again and came close to breaking the deadlock when Luke Mulholland hammered an effort at goal, but Kwarasey made a fine stop to turn the ball away.
In the second half, Alvas Powell had an opportunity to find the net for the visitors when he won the ball and raided into the box, but his strike sailed over the bar.
Garcia threatened again for Salt Lake when he was allowed space on the edge of the box, but Kwarasey got down low to make the save.
The Timbers pushed for a winner late in the game as Maximiliano Urruti curled an effort at goal, but Nick Rimando pushed the ball to safety.
Portland won the match right at the death as Borchers turned the ball past Rimando to snatch the three points for the visitors against his old club.