Fanendo Adi continued the magical start to his Timbers career and led the team to a third win in four games.
The home team put a number on the board first, with Luke Mulholland turning and lashing in a loose ball following a 23rd-minute corner kick.
Portland responded with a brace from Fenando Adi to take a lead into halftime. The Nigerian used his height to knock home Diego Valeri's 36th-minute corner before tapping home an easy rebound after Darlington Nagbe's shot was saved hyst before the break.
RSL defender Tony Beltran was sent off in the second half as he picked up a pair of yellow cards in as many minutes for a pair of rash fouls on Nagbe.
The Timbers scored their first penalty of the season in the 73rd to cap off the result. Chris Shuler was called for a handball in the box and Will Johnson did the honors against his former club.
After starting 2014 with a 12-game unbeaten run, Real Salt Lake now finds itself on a four-match winless slump with two losses in its last three games. Portland, which needed nine games to find victory, has won three of its last four.