Rowland Hall (15-2) had beaten Waterford (13-2-1) twice this season, both times by one goal, and the Winged Lions dominated control of the ball until the midway portion of the first half.
But the Lions couldn't get the ball past Waterford senior keeper Lexi Shreeve, who began playing in goal this year after three years as a midfielder.
And then came Mumford's header in 18th minute that put Rowland Hall on its heels. On a shot by teammate Samantha Morris, Mumford altered the ball's path enough to give Waterford a 1-0 lead at Rio Tinto Stadium.
"I was just kind of hanging back with the line and I saw the ball come off her foot," Mumford said. "I heard a defender behind me say 'mine,' but I knew I could get to it.
"It was just the littlest flick off my head, so that the keeper couldn't get it," she added.
With 8:15 left in the first half, Waterford got a second goal when Ritzman launched a shot from 25 yards away from the right side of the goal. Rowland Hall goalie Allison Bagley seemed taken aback as she struggled to contain the high shot, which deflected off her and into the net.
"In our first game, Angelina Peterson scored on a ball that was really far away and I just decided to take the shot," Ritzman said.
It's Waterford's first championship since 2012.
Rowland Hall was a more recent winner, taking the 2A championship in 2014, but Lions coach Bobby Kennedy said that Waterford's tradition still holds sway over the small-school classification.
"They have a mystique about them that we're still trying to counter a little bit," Kennedy said. "But I thought we came out pretty good. We're young and it showed a little bit in the playoffs.
"We knew they would do well on the counter-attack and well on the set plays," he added. "They sat back a little more than we thought. I've been playing them for 10 years and had never seen them sit back so much."
Waterford scored its second goal, on only its fourth shot. Another one of the four, also by Ritzman, had deflected off the top bar.
Once the Ravens had the two-goal cushion, their defensive posture went into full-force.
"We knew we had to contain two players of theirs [Jordan Crockett and Airam Perez] that had really hurt us in the regular season," Waterford coach Tim Dolbin said. "In that respect, it [was] much, much more clamped down for them and not as open.
"We knew we'd get our chances too and we finished them," he said.
Waterford 2, Rowland Hall 0
R Waterford gets goals from Makenna Mumford and Tanner Ritzman in the first half and a shutout from keeper Lexi Shreeve for the victory.
• Rowland Hall had defeated Waterford twice in the regular season, in region play, by one goal each time.
• It is the Ravens' fifth state championship overall and their first since 2012.