Portland remains barely alive in the playoff chase thanks to a 1-1 draw which eliminated D.C. from postseason contention.
Portland grabbed early control of the match and, 24 minutes in, took the lead. Kenny Cooper got in behind the United defense to head home a Rodney Wallace cross from close range.
The home team came out in the second half knowing it needed two goals to save its season and started to commit men forward. The Timbers were content to sit back and absorb pressure, attempting to hit back on the counterattack.
"The basis of my pregame speech: 'Let's go down swinging,'" D.C. coach Ben Olsen said.
MVP candidate Dwayne De Rosario gave his side a lifeline in the 73rd minute with an excellent turn and left-footed finish in the box which beat Perkins to his near post. The goal was his 16th of the season and put him alone in first place in the Golden Boot race.
Portland substitute Brian Umony had a pair of golden chance to win the match in the last 10 minutes.
Together the teams combined for 13 shots in stoppage time, and 24 after the 77th minute, according to Opta, in a hectic and pulsating end to the match.
"It was a bit of a blur, that last 20, 30 minutes - in fact the whole second half - but I was extremely proud of the guys tonight," Olsen said. "I can't believe nobody scored down that stretch."