Justin-Siena High School threw just about every chapter of its defensive playbook at Branson-Ross, the defending CIF state girls basketball champion.

In a battle of unbeaten Marin County Athletic League teams, Justin-Siena was relentless on the defensive end, switching up its attack and stifling Branson to the tune of just 11 points in the second half.

The Braves used an 8-0 run bridging the third and fourth quarters to take control and went on to win, 48-37, gaining sole possession of the league lead in front of a near-capacity crowd at Clark Gym Tuesday night.

The victory was the eighth in a row for Justin-Siena (15-1 overall, 6-0 MCAL), ranked 14th in the Cal-Hi Sports Bay Area poll and 15th in the San Francisco Chronicle’s Top 20.

Despite being double- and triple-teamed, Vicky Deely scored 25 points and had 15 rebounds and four steals. Britney Hyatt also played very well with 11 points, five assists and four steals as the Braves came from five points behind at the end of the first quarter (15-10).

“Defensively, I just think the kids played phenomenal,” said coach Mike Boles, whose team was in man-to man, zone and some other defenses that shut down Branson (11-6 overall, 5-1 MCAL). “They really understood who we needed to shut down and they really focused on the defensive end. We threw a lot of different defenses at them. We probably didn’t go consecutive defenses for more than three defensive possessions. We tried to mix things up a lot.

“(Branson’s) well-coached. We didn’t want to show a tendency.”

Branson, a Division V school, had its 35-game MCAL winning streak broken. The Bulls, who were led by Lauren Polansky with 13 points, seven steals, seven rebounds and five assists, hadn’t lost a league game since the 2005 season.

“This is a huge win,” said Hyatt, whose 3-point play at the 6:44 mark of the fourth quarter gave Justin-Siena a 42-33 lead. “We were just really geared up for the game mentally and physically. We got out there and did our best and it paid off. We’ve worked so hard to get here.”

The Braves had great balance from their lineup, as Courtney Pardini had eight points, five rebounds and four steals; Kyleigh McAhren had five rebounds and three steals; and Jessica Futo had seven rebounds and three assists. In addition, Deely was 9-for-10 and Hyatt 5-for-7 from the free-throw line.

Justin-Siena’s momentum-changing 8-0 run was keyed by Hyatt’s free throw, which gave the Braves a 36-33 lead; Deely’s two free throws with 16 seconds to go in the third quarter that gave Justin a 38-33 advantage; a Deely basket to start the fourth period that increased the lead to 40-33; and Hyatt’s basket and free throw at the 6:44 mark.

“Our defense was the biggest factor in that,” Hyatt said of the Braves’ second-half surge. “As a team, we talk on defense a lot and get easy steals and easy baskets.”

A shot by Polansky cut Justin-Siena’s lead to eight with 5:37 to go, but the Braves responded with a 5-0 run. Futo and Pardini tuned up the defensive pressure on Polansky.

“We went in, we executed, we played as hard as we could, we played with heart, we left it all on the floor with no regrets and it paid off,” said Deely, who came into the game averaging 22.1 points and 10.0 rebounds per game. “We looked to set screens, we looked to run our offenses, we looked to reverse the ball, and attack the basket. That was our key point going into the game: attack the basket early.

“We definitely kept switching up defenses, which got us that momentum going into the third and fourth quarter, so we were able to get steals. Boxing out was key. We got rebounds. We looked up the court. We got good shots, so that was key to executing.”

Branson was without two of its top players, sisters Rachael Bilney and Samantha Bilney, who are injured. Rachael Bilney had 14 points, five assists and five rebounds as Branson won the girls Div. V state title game, 51-36 over Pacific Hills-West Hollywood last March at Arco Arena in Sacramento. Samantha Bilney had 12 points and eight rebounds for Branson (33-3), last year’s MCAL champion which ended the year on a 31-game winning streak.

“They’re a good basketball team,” said Boles. “We also recognize the fact that the Bilney sisters aren’t there — but it does not take away from the win. I’m just really proud of the way the girls came out and executed our game plan offensively and defensively.

“I told the kids to enjoy it. They work hard at practice, and that’s where that game is won. We’ve got great senior leadership, which lends that maturity to our basketball team. I couldn’t be prouder of 13 kids.”

Boles was also pleased with the way his team was able to show patience with the ball and see what the defense was doing.

“We’ve got some very good basketball players, so if we can just stop the ball, read the defense, they’ll make the appropriate play,” he said. “I think we played a little too fast to start the game.”

Branson, ranked No. 8 by the San Francisco Chronicle, also had a seven-game winning streak broken. Akana King had eight points and Michela Bestwick seven points for the Bulls, the No. 1-ranked Division V team in the state by Cal-Hi Sports.

“We’re definitely at the top of our game right now and we want to keep going like that,” said Deely. “We want to attack every opponent we play with just as much energy and just as much heart.”

Varsity Boys

• Branson boys 66, Justin 29

James Thompson had 12 points, Kevin Morinec had five points and Trevor Leveque four for Justin-Siena (7-10 overall, 0-6 MCAL) in Tuesday’s game. The Braves were without four players — Kevin Dougherty (ankle), Pat Lazzari (ankle), Brad Aden (ankle) and Justin Clayton (illness). Dougherty, one of the top scorers in the Napa Valley, has an appointment with an orthopedic surgeon Thursday. Eight players suited up for Justin-Siena.

“I thought the eight kids played extremely hard,” said coach Phil Rosemurgy. “They did the best they could. We’re struggling right now. But I was really, really proud of the kids that played. I was happy with the bench.”

Branson (14-3 overall, 5-1 MCAL) was led by Ryan McGuigan with 11 points, Oliver McNally and Tyler Killups with 10 each, Adam Boone with eight, Kalome Akhile with six, Tim Gaumond with five, and Cyrus Stutts with four.

“They shoot the ball very well,” said Rosemurgy. “They didn’t do anything to take us out of our offense. We just didn’t shoot the ball very well.”

Branson beat View Park Prep-Los Angeles in overtime in the boys Div. V state title game last March, 57-48. Branson (33-2) won its second straight state title and was making its third straight appearance in the championship game.