Rimando made six top draw saves in the rain in Portland and watched a number of other shots flash wide of his goal, as the Timbers were forced to settle for a scoreless draw in the penultimate round of the regular season, significantly weakening their bid to qualify for the play-offs.
It was a game for the men in goal with Donovan Ricketts also making three top saves for the Timbers.
The draw saw Portland move ahead of Vancouver Whitecaps into the top five of the Western Conference.
But with Vancouver set to play cellar-dwellars San Jose Earthquakes on Saturday, the Timbers could easily fall three points behind the Whitecaps by the end of the weekend with one game left for each side.
Portland dominated at Providence Park - particularly in the second half - but whenever they got a shot on target, Rimando or one of the United States international keeper's team-mates denied the home side a crucial goal.
Rimando's best save came in the 61st minute.
Portland playmaker Diego Valeri saw his shot blocked by a RSL defender, although Rimando went to ground in preparation to make a stop, but as Darlington Nagbe struck the rebound, the 35-year-old custodian got up to smother the shot, before Rodney Wallace also had an effort blocked and Fanendo Adi stabbed his follow-up effort wide.
Soon after, RSL's Luis Gil blocked Portland defender Norberto Paparatto's header from a corner on the line.
Real substitute Alvaro Saborio almost made the Timbers pay with 12 minutes remaining but just sent his shot over the bar.
But it was Portland that made all the running to finish the contest as visiting defenders made a number of desperate blocks, before the Timbers' Maxi Urruti hooked a cross across the face of goal - and just out of reach of any team-mates - in second-half stoppage time for the final decent chance.
The 0-0 draw is a big blow to the Timbers - who topped the West last season - as their fate is now out of their hands with Vancouver knowing they need four points over their last two games to secure a play-offs berth.
The Whitecaps will play two teams outside the West's top five to finish the regular season - San Jose and seventh-placed Colorado Rapids.
The draw took Real to 53 points - third in the Western Conference behind Seattle Sounders and Los Angeles Galaxy.
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