The Dash now have five goals, most of any team in the tournament.
Mewis scored in the 12th minute, taking a sweet back heel pass from Shea Groom and blasting the ball from just inside the penalty area.
Groom scored on a precisely executed leaping header in the 54th minute. It was her second goal of the tournament.
Rachel Daly scored two goals in Houston’s opening game, a 3-3 draw with the Utah Royals. She was listed as questionable for the game against