Schmelzel and Valenzuela had a 13-under 197 total at Midland Country Cup heading into the better-ball final round. They opened with an alternate-shot 68 on Thursday and had a best-ball 61 on Friday.
"You're kind of on pins and needles most of the day, just hoping you don't get your partner in trouble," American Schmelzel said.
"Just super solid. I feel like we had really good attitudes throughout the entire day. I think both of us took every single shot as it came."
The teams of Jin Hee Im-Somi Lee (68) and Manon De Roey-Pauline Roussin-Bouchard (69) were a stroke back.
"I'm very proud of us," De Roey said.
"We hung in there. We fought until the end."
Jennifer Kupcho and Leona Maguire, the second-round leaders after a 60, birdied the final two holes on Saturday for a 72 that left them tied for fourth at 11 under with Lauren Hartlage-Brooke Matthews (66) and Sung Hyun Park-Ina Yoon (67).
"Just try and go low and try and post a number early and see what happens," Maguire said.
"I think it was nice to see two putts go in at the end."
Lexi Thompson-Meghan Kang (68) and Rio Takeda-Miyu Yamashita (67) were 10 under.
Defending champions Ruoning Yin and Jeeno Thitikul (67), both among the top five in the women's world ranking, were nine under along with Australia's Cassie Porter and Scot Gemma Dryburgh (73).
Schmelzel and Valenzuela parred the final seven holes. They had four birdies and two bogeys in the round.
"I feel like we had a really good day," Switzerland's Valenzuela said.
"Our goal in foursomes was just to get a couple under or maybe a little bit better. We had a few mistakes, and that's going to happen in this format. We also did a lot of really good stuff."
