Clark's goal that gave the Dynamo a 1-0 lead in the 34th-minute looked like it was going to stand until nine-men Vancouver gave away a corner late in the match. Houston converted to seal it up three minutes before the 90th.
Here's how it happened:
We start with the relatively few amount of players in the box before Brad Davis strikes the ball.
Raùl Rodríguez (farthest to the left in orange) starts closer to the penalty spot. Sam Adekugbe (second Vancouver player from left) is ahead of him.
The Whitecaps are man-marking rather than zonal marking, making it seem like Adekugbe isn't on the same page as his team because he is farther away from Rodríguez. He also could be anticipating a low ball to the Spaniard and is planning to step up and intercept it, though that seems unlikely with a defender standing at the edge of the six-yard box to defend exactly that.
Here we see the Dynamo players beginning their runs into the goalmouth.
Six out of nine Vancouver players are back on defense marking five Dynamo attackers. Not surprisingly they are focused on getting a counter-attack going rather than preventing goal.
The ball comes into the picture and it is in the air toward the near post, not what Adekugbe was looking for.
Rodríguez goes up for the header unmatched. This should not happen. Adekugbe doesn't do his job at all here.
Rodríguez puts a beautiful header into the far corner of the goal, rendering David Ousted helpless.
The plan for the Dynamo was most likely not for Rodríguez to shoot. Usually, near-post corners are meant for a player to flick it on to the far post, whether it be a header or a kick. Houston had a man running far post that was probably ready to put home Rodríguez's flick.
But when Adekugbe didn't go up for the header, the Barcelona-native felt he could put one on goal and he did exactly that with a very nice header.