Johnson leads the Timbers with eight goals.
Only two minutes later, Mauro Diaz scored his first goal for FC Dallas to even it. Ricketts slid to the turf out in front of the goal, allowing Diaz to take advantage.
Diaz, who is from Argentina, was acquired by FC Dallas last month and had appeared in just one match for the team as a reserve before his start Saturday night.
Nagbe's goal, off an assist by Valeri, gave the Timbers the lead back — for good, as it turned out.
Valeri has had an assist on each of Portland's last six goals, and is the first Timbers player with 10 assists since the team joined MLS in 2011.
"We are a very good attacking team and I try to help," Valeri said. "I try to do my role."
The match featured a flurry of yellow cards in the second half, with Portland's Valeri and Ben Zemanski and Dallas' Jackson and Blas Perez each called for a yellow in the span of less than five minutes.
"I don't know if it was getting more physical, I just think the yellow cards started coming out," Hyndman said.