The home side started the game strongly and could have been ahead in the seventh minute when Steven Lenhart picked up a loose ball outside the area and volleyed at goal, but Donovan Ricketts made a good save.
Ricketts was in action again minutes later as he produced another great stop this time to deny Chris Wondolowski, tipping his effort over the bar after the striker had been put through by Shea Salinas.
The Earthquakes were almost level immediately as Marvin Chavez lifted a free kick into the penalty area and Mikael Silvestre nearly headed the ball into his own net, but fortunately for the defender it went just wide of the post.
Sam Garza then wasted another glorious chance for the hosts as he picked up the ball and drove into the box, but at the final moment he lost his composure and scuffed his effort.
The hosts continued to press for an equaliser and they finally got their breakthrough in the 92nd minute when Jahn fired past Ricketts into the bottom corner of the net.