The draw snapped Portland's eight-game home win streak against the Earthquakes, which was tied for the longest active home winning streak against a single opponent in MLS (Union vs D.C.).
The game was a rough-and-tumble affair, with Diego Charra being sent off for Portland after a second yellow card two minutes into second-half stoppage time. The bad blood spilled over into the postgame, when a shoving and shouting scrum continued for several minutes.
The draw allowed the Earthquakes to extend their unbeaten streak to six games, though they have only one win since May 7 (six losses and six draws).
Portland is winless in its past three games and has won just twice in its last seven outings.
Lopez found the net in the 24th minute for San Jose after Cristian Espinoza's shot was batted down by Timbers' goalkeeper Steve Clark. The rebound landed right at the feet of the wide-open Lopez, who converted the easiest of goals to give the Earthquakes the early advantage.
The Timbers leveled it in the sixth minute of first-half stoppage time as Felipe Mora scored from the ground after a corner kick by Yimmi Chara was headed into the box by Bill Tuiloma. San Jose keeper JT Marcinkowski got a hand on Mora's volley but could not keep in from going across the line.
Two stops on point-blank shots by Portland backup keeper Aljaz Ivacic, who entered late in the first half after Clark suffered a groin injury, kept the game tied.
Portland dominated the statistics, outpossessing the Earthquakes 58.5 percent to 41.5 percent, outshooting the visitors 21-13, and leading in total passes (455-321), passing accuracy (84.8 percent to 71.7 percent), corners (6-4) and crosses (23-14).