Arianna Cardenas hadn’t scored in more than a month, and she was battling a freshman for minutes, but few have been better in big games.

East Union head coach Victor Polanco trusted his instincts, inserting Cardenas into the starting lineup, and the second-year coach was rewarded.

The junior pounced on a loose ball near the top of the 6-yard box, slipping it inside the near post for the tone-setting goal in a 3-1 victory over No. 4 Oakdale in the Sac-Joaquin Section Division III semifinal.

Ilena Rivera continued her remarkable sophomore season with two second-half penalty kicks as the top-seeded Lancers (19-0) moved one step closer to another section title.

East Union won the Division IV crown a season ago with a 3-2 victory over Vista del Lago. One of the heroes in that game was Cardenas, whose header in the 39th minute was the eventual game-winner.

She was up to her old tricks again on Wednesday evening, finding the back of the net for the first time since March 30.

“I’ve been trying,” Cardenas said with a chuckle. “I’ve been shooting and shooting, but they haven’t been going in.”

The goal was a testament to her determination — and a knuckling blast by stopper Bella Cardenas, who launched her shot from well over 25 yards out.

The movement of the ball seemed to baffle Oakdale goalie MacKenzie Weiglein, who took the shot off her stomach. Weiglein recovered quickly, pushing back Rivera’s follow-up.

The ball found Cardenas’ foot, and she calmly slotted it inside the post for a 1-0 lead in the fifth minute.

“I was pretty excited because I didn’t think it would go in. I thought the goalie had it, but it slipped right in,” Cardenas said. “Whenever we’re in our groups (in practice), we always tell each other to follow our shots, to always be there because goalies let go sometimes.”

Cardenas was thrust into the starting lineup on a hunch. Polanco had a feeling Cardenas’ physicality would create problems for Oakdale’s defense.

He was right.

“I made a switch, because I know Oakdale is physical on the back. Those girls play physical and Arianna Cardenas can take any of them,” Polanco said. “She’s always ready for these big games.”

Rivera punctuated the victory with two penalty kick goals in a five-minute span. She went to the right of reserve goalie Melissa Ibarra each time, striking the freebies high and hard. The penalties were created by a pair of knifing runs by Jenna Zuniga and Rivera.

Zuniga was pulled down in the box after splitting two defenders with her dribble in the 48th minute.

Five minutes later, Rivera went around her defender and raced on goal. She was tackled hard from behind just as she was about to shoot.

Rivera praised Zuniga, a fellow sophomore and near-lifelong friend, for creating the separating goal.

“She knows the game well. She knows if she beats this player here, they’re going to have to dive in,” Rivera said. “Once you get into the box, (the defense) is just trying to get the ball. If you toe-poke it around, you’re either going to get the ball back or they’re going to foul.”

Oakdale (16-8-4) fouled and paid dearly, losing for the third time in the last four games against the Lancers.

Ashley Arnett notched the Mustangs’ only goal on a penalty kick in the 71st minute. She is tied with Ripon Christian’s Abby Buitrago for the state lead in goals with 42.

East Union has won 24 consecutive games. Polanco said his team is “hungry” for a second straight section crown and first at the D-III level.

To seal the deal, though, East Union will have to beat another Valley Oak League rival for a third time this season.

Across town, Manteca (22-4-1) booked its second straight trip to the Division III final with a come-from-behind 2-1 victory over Ponderosa.

News of the Buffaloes’ victory was announced with about two minutes left. East Union swept the season series, winning 2-0 and 1-0.

The game will be played at Lincoln High in Stockton Saturday starting at 2 p.m.

“I’m not afraid,” Polanco said. “We’re going to go and play the game.”