Just before the break Houston got their equaliser. Brad Davis lifted a cross into the area and Clark rose highest in the area to head the ball past Seitz.
After half time, the Dynamo were reduced to 10 men when David Horst was given a straight red card for a challenge on Fabio Castillo.
From the resulting free kick, Dallas retook the lead in the 61st minute. Diaz whipped a dangerous ball into the box and Watson beat his man and headed the ball low past Hall.
The visitors were beginning to up the ante to kill the game and got their third goal when Michel's corner was headed into his own net by Barnes as he jostled with Watson in the area.
Dallas sealed their win when Diaz threaded a through-ball for Watson to put him one-on-one with Hall and he made no mistake in slotting the ball past the keeper for his second of the match.