The Dominicans, beaten 14-0 by the United States after allowing a goal 38 seconds after kickoff on Friday, didn't relent until the 21st minute, but rarely managed any possession in the offensive half and attempted only one shot in the first 45 minutes.
Mexico won its second straight and improved to six points in Group B.
With a match against the United States looming on Tuesday, Mexico coach Leonardo Cuellar made nine changes to his starting lineup from Friday's opening 5-0 win over Guatemala. He was without forward Renae Cuellar, who the Mexican federation said was threatened by the University of Arizona with not graduating if she didn't return to school.
Cuellar used only Marylin Diaz and Teresa Noyola from the starting lineup against Guatemala, and also inserted 15-year-old Chrystal Martinez, who was one of two Mexicans to hit the post.
"I decided to give rhythm to the rest of the players and also because it's a young team," Cuellar said. "So they need to experience these scenarios, they need to step up. What happened today gives me a better idea of how I'm going to balance the next two games, who responds well to the pressure."
Diaz and Rosario Saucedo also scored for Mexico, which will now look to its game with the United States, a rematch of its upset win in the semifinals of the 2010 CONCACAF World Cup Qualifying in Cancun, Mexico.
Mexico pressed from the outset and had a header by Martinez go high 54 seconds into the match and a header by Ariana Romero loop into the arms of Domincan keeper Heidy Salazar before two minutes had elapsed.
El Tri went ahead when Noyola recovered the ball in midfield and sent it to Diaz. She beat defender Dominican defender Carmen Polanco and scored from just outside the goal box. Diaz doubled the lead in the 27th, converting a penalty after Yaquesi Nunez left her feet and lunged from behind to bring down Saucedo.
Ruiz increased the lead to 3-0 in the 38th trading passes with Guajardo, getting around defender Ana Diaz and finishing from the edge of the six.
After Mexico outshot the Dominican 19-1 in the first half, Guajardo scored all three of her goals after the intermission --- in the 49th, 62nd and 75th minutes, and Ruiz added her second in the 70th.
"I think that anyone can do what I did today any one of these players," Guajardo said. "It's just my lucky day I guess, but the girls on the bench and the girls on the field they keep the rhythm of the game, they keep the momentum high and that's what makes it so great."
The Dominican Republic, which didn't allow a goal in three Caribbean qualifying games, have been outscored 21-0 in two matches at the CONCACAF finals and has a match Tuesday against Guatemala remaining.