With time running out, Jahn got control of the ball in the center of the box and fired home a shot from 12 yards out, slotting a right-footed shot past Donovan Ricketts.
The late tally, Jahn's second the year, enabled the Earthquake (2-3-3) to extend their streak of regular-season MLS games without consecutive losses to 52 contests.
Diego Valeri found the net in the 58th minute for the Timbers (2-1-4), who ran their unbeaten streak to five consecutive matches.
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