Clark followed Will Bruin's rebounded shot after United goalkeeper Andrew Dykstra's initial save. Dykstra's deflection fell to the middle of the box, leaving an open net for Clark to smash home his second goal in two games.
The Dynamo (2-2-3) improved their unbeaten run to four of their last five.
Chris Rolfe opened the scoring for United (3-1-2) in the 36th minute, slotting a free kick just inside the top right corner of the goal from 24 yards. Dynamo goalkeeper Tyler Deric managed a slight touch on the ball before it glanced in off the inside of the post.
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