CONCORD >> The buzzer sounded as St. Mary’s-Stockton guard Mia Jamias’ meaningless shot fell helplessly to the floor. The Carondelet Cougars rushed the floor, encircling the starting five in celebration. Dancing. Cheering. Hugging. All while tears streamed down the faces of their opponents.

Carondelet is headed to the CIF State Division I championship game.

“It was a tough battle,” Carondelet coach Kelly Sopak said. “We got behind in the first quarter. It was tough to have to battle back. But we did it.”

The third-seeded Cougars’ 56-51 win over No. 4 St. Mary’s on Tuesday was the byproduct of controlling the ball, relentlessly attacking the rim, pouncing on the offensive glass and ultimately wearing down the visiting Rams (20-14).

The Cougars (29-6) head to the Golden 1 Center in Sacramento to face Sage Hill of Newport Beach (23-11), the Southern California champion, on Friday at 7 p.m.

The star of the night was Niylah Christopher. The 5-foot-9 freshman forward led the Cougars in scoring with 12 points and made her presence felt among the bigs on the floor — including 6-foot-4 St. Mary’s center Evelini Smith and 6-foot-1 Carondelet center Celeste Alvarez. Christopher handled the ball in pressure situations when her team needed and attacked the rim. Every offensive rebound she corralled seemed to hurt St. Mary’s.

“I’ve always been the smallest person on the court,” Christopher said. “But, I’ve got that dog mentality. So no matter what, I’m gonna come down with the ball. Tonight, I put on for my team.”

Sopak lauded his freshman’s effort and impact on the game.

“She’s a 14-year-old senior,” Sopak said. “She’s just phenomenal. It’s been a great boost for us.”

Layla Dixon added 11 points for Carondelet and Alvarez scored eight points while guarding Smith, the Rams’ best player.

After being down early, Carondelet took control of the game in the third quarter and held a nine-point lead entering the fourth. The Cougars were eight minutes from their first Northern California title since 2010 when they won the Division II NorCal section. They just needed to hang on.

Back-to-back three-pointers from Rams guards Theresa Gotico and Jamias cut the Cougars’ lead to four points with just under five minutes remaining. Kori Rogers tried to answer with a three for the hosts, but Christopher collected the miss and scored the putback to put Carondelet head by six. After a back-and-forth few minutes, a bad turnover with two minutes left from St. Mary’s allowed Carondelet to assume full control.

It was the Cougars late-game execution and free-throw shooting — they made five of eight from the line — that sealed them the game. But it was their relentless effort, led by Christopher, that won them a regional championship and left St. Mary’s and head coach Alle Moreno bewildered.

“I don’t know,” Moreno said. “And that’s going to haunt me for a very long time because that was one of our keys. But I thought they were really relentless on the boards and that’s the winning mentality you got to have in these big games. You gotta leave it all out there. That was the difference in the game because I know they got a lot more than five offensive rebounds.”