It was the Lady Tigers' first win over The Woodlands, which was also ranked No. 6 in ESPN RISE's national poll.
"This was a 100 percent team effort," Belton coach Barry Elkins said. "That's really the statement we wanted to make."
The Woodlands had outscored its first three opponents 21-0 but was held to just one goal by Belton's tough defense.
"They really stepped up," Elkins said. "I was really pleased with the back line."
The Lady Tigers got on the board in the fifth minute on freshman Jaime Boone's goal off an assist by junior Jourdan Brown. Belton retook the lead in the 20th minute on an unassisted goal by senior Taylor Pressley.
Belton's scheduled game against Round Rock McNeil was forfeited.
The Lady Tigers open play in the Round Rock Tournament on Thursday against Dallas Highland Park.
