Sierra High opened Monday’s Sac-Joaquin Section Division III playoffs with a convincing 7-1 victory over visiting Pioneer.

The No. 8 seeded Timberwolves (15-9) overcame a rough patch at the start of the game by scoring four times in the fourth and adding three in sixth.

“Those three runs were big,” said Sierra coach Jack Thomson.

His team will travel to Sacramento on Thursday to face top-seeded Christian Brothers (25-1) at McAuliffe Memorial Ballparks. First pitch is set for 7 p.m.

Timberwolves starting pitcher Jacob Peterson picked up the win over the No. 9 Patriots (12-16) of the Tri-County Conference. The junior right-hander allowed a run, four hits, three walks, and three strikeouts.

“JP was able to get out of some trouble,” Thomson said.

In particular, he was referring to the first inning where Peterson loaded the bases on a walk, hit and an error.

“That was uncharacteristic of us,” Thomson added.

Still, Sierra got out of that jam unscathed.

“We came out a little nervous,” said Peterson, who got plenty of run support in the fourth.

Hunter Frisk led off with a single and was replaced on the base path by Mateo Molieri. Jesse Babauta also singled, with he and Molieri moving up on Peterson’s nicely placed bunt.

Freshman Zach White drew a bases-loaded walk.

With designated hitter Marcos Castillo at bat, Molieri scored the game’s first run on a wild pitch. Babauta came home on an error and JT Ortiz-Martinez’s RBI single plated White.

Castillo scored the fourth run on Jaden Pina’s double.

Pioneer chalked up its lone run in the fifth. Chris Irby’s sacrifice fly delivered Alex Rudi, who had a lead-off double.

The Timberwolves added some insurance runs in the sixth when White, Kenny Wade — he pinch ran for Ortiz-Martinez, who reached base on an error — and Pina scored. Chase Sperbeck and Frisk, who was 2 for 3, had an RBI single each.

Peterson closed out game similar to his start — loading the bases but working his way out of the jamb.

“I was real happy to get this one out of the way,” Thomson said.