STOCKTON — It took the smarts of a sophomore and a gutty effort from a freshman pitcher to get Sierra High to its first-ever Sac-Joaquin Section championship-round appearance.

No matter what happens in today’s Division-IV finale, the future looks blindingly bright for the Timberwolves.

Elia Vasquez drove in the go-ahead run in the top of the eighth inning, and Allison Walljasper battled through a sore arm to strike out two batters in the bottom half and secure a 2-1 victory over Cosumnes Oaks of Elk Grove at Arnaiz Softball Stadium Friday.

“I feel horrible right now, but I’m just going to keep on going until we get this championship. I’m really determined to get it done for the team,” said Walljasper, hampered by arm and shoulder issues since leading Sierra to the NorCal Classic Platinum Division championship in the final weekend of April.

Cosumnes Oaks (19-12) went on to lose to Los Banos 8-2 in the consolation semifinal Friday night. That sets up a rematch of a quarterfinal contest in which Sierra edged Los Banos 1-0 on Thursday.

Los Banos (21-10) beat Oakdale 5-4 in eight innings earlier Friday.

The Division-IV final gets underway at 11 a.m. today and again at 1 p.m. should Los Banos win the first contest.

Daylynn Penner led off the eighth inning for Sierra (25-1-1) and reached on a two-base throwing error. Sommer Wilson bunted her to third for the second out to set the table for Vasquez.

In her previous at-bat, Vasquez looked at a called third strike — a change-up from Cosumnes Oaks pitcher Maddy Fish — to end the sixth inning.

That provided Vasquez a blueprint for her next time up. She took a hack on the first offering and belted it to left field to plate Penner.

“I waited on her changeup and went with it,” Vasquez said. “I had a changeup on the last pitch, and I was assuming that they were going to give me another one. I was ready for it just in case.”

Sierra was able to win despite recording just three hits. The other two were leadoff singles from Wilson and Lily Gonzales in the fourth and fifth innings, respectively.

Gonzales was driven in by Iyana Hughes’ sacrifice fly to left, which tied the game at 1.

The Wolfpack struck in the opening inning. Melia Roberts doubled to lead off, and a misplayed ball in the outfield on Clarissa Beverly’s base hit up the middle allowed her to score.

All three runs plated were unearned, and Cosumnes Oaks committed five errors.

Walljasper has yet to give up an earned run in her first postseason campaign. The Timberwolves opened with a 2-1 win over Central Catholic of Modesto on their home field Wednesday.

Walljasper’s stat line was modest Friday: eight strikeouts, seven hits, one walk and one hit batter. By comparison, the Wolfpack’s Fish finished with 12 strikeouts to three walks in her three-hit effort.

How she played through the pain in pressure situations render those numbers moot.

“She doesn’t have 100 percent of her stuff, but even at 50 percent she can mix it up well and pitch her changeup for location,” Sierra coach Nick Olmo said. “She still has enough to where she can throw some smoke when she has to, but we were trying to keep that down to a minimum.

“I think she did a great job. The kid’s got a ton of guts for a freshman. She shows a lot of composure up there.”

Had Sierra lost, Olmo said he would have likely gone with another pitcher for the do-or-die semifinal. That would have left either Jackie Deanda or freshman starting catcher Lexus Barnes as options to man the circle, and they’ve pitched a combined five innings this season.

Walljasper made the decision for Olmo by shutting the door in the eighth.