The semifinal showdown between the two best teams in San Joaquin County lived up to the hype on Friday, but anyone expecting a showcase of explosive offenses may have come away disappointed.

This one came down to defense, and visiting St. Mary’s shut out top-seeded Manteca in three quarters on the way to a 19-14 upset at Guss Schmiedt Field. The fourth-seeded Rams of Stockton (10-2) will face No. 2 Granite Bay next Saturday, Nov. 29 in the Sac-Joaquin Section Division II championship at Sacramento City College.

Manteca (11-1) and St. Mary’s entered the game ranked second and fifth overall in the SJS by MaxPreps computer ratings while boasting two of the most explosive offenses. The Buffaloes could not get untracked in the first half, however, and their last drive in the final minute ended with four incompletions.

“The best team did not win tonight,” Manteca coach Mark Varnum said. “We just made too many mistakes in crucial moments. That’s why it’s over.”

The Buffaloes had two chances to put it away. They led 14-7 and had the ball on the St. Mary’s 40-yard-line when quarterback Owen Gully fumbled the handoff to Nikko Juarez. Luke Lucatello recovered the loose ball for St. Mary’s near midfield with 7:38 remaining.

The Rams capitalized on the opportunity, scoring on a 1-yard keeper Jaden Galvan. They opted to go for the lead on the conversion try but fumbled the handoff. St. Mary’s still had 3:34 to go while trailing, 14-13.

“They were out of timeouts, and we felt like we needed to put some pressure there,” St. Mary’s coach Tony Franks said. “We need to win it at that point — you don’t play for the tie at somebody else’s house. And the way things were going, we felt like we needed to get the two-point conversion. We didn’t execute it, but we still had all three of our timeouts with 3 minutes and 34 seconds left, so there was a lot of time.”

The gamble may not have paid off immediately, but Franks had trust in his defense.

Manteca went three-and-out on the next drive, taking just 15 seconds off the clock.

St. Mary’s did not end up needing all that time to jump ahead for good.

On the next play from scrimmage, Galvan, with pass rusher Robert Nelson chasing him out of the pocket, spotted Jeremy Krause for a 55-yard touchdown pass. It was a redemptive moment for Krause, who earlier dropped a sure touchdown on the Rams’ first drive of the game. They did not end up scoring on that opening series, turning it over on downs in the red zone.

Manteca had three drives stall inside the opponent’s 20 and limited the Buffaloes’ offense to 73 yards in the first half.

“Our defensive kids the last few weeks took it on the chin, and it got a little personal,” Franks said, referencing St. Mary’s 64-55 thriller over No. 5 Jesuit in the opening round as well as its 54-41 triumph at rival Lincoln in its regular-season finale.

“They decided they were going to play better. We wanted to play good, fundamental defense and get after Manteca’s offense up front. We challenged our kids to do that, and our Coach Blake Eagal, our defensive coordinator, and his staff did a great job of dialing up a game plan.”

Manteca did get its offense going in the third quarter, using seven straight run plays on the first drive of the second half to finally get on the scoreboard. Juarez capped it off with a 4-yard run, finsihing with 84 yards on 21 carries.

“Just had to get back to getting big and nasty,” Varnum said. “Had a great drive there, but we just couldn’t really get anything going after that. We were behind the sticks a lot all night, and that’s not our game.”

Gully completed 13 of 27 passes for 143 yards, and standout receiver Quinn Martinez tallied 10 catches for 70 yards.

Defensive back Jayden Harris accounted for the Buffaloes’ other touchdown, a 25-yard pick-six that — coupled with Gully’s conversion pass to Martinez — gave them the 14-7 lead with no time left in the third quarter. The interception is a section-leading ninth of the season for Harris.

“Couldn’t be more proud of the defensive effort tonight,” Varnum said. “All season, the defense carried us, and they almost did it again tonight.”

Kyrin Barajas paced the Buffaloes defense with eight tackles, while Mathieu Evans contributed six tackles, two sacks and a pass break-up.

Manteca limited UCLA-committed receiver Kenneth Moore III to two catches and 11 yards and minus 1 rushing yard, but the Rams have more than enough weapons to make up for it.

Galvan (15 of 29, 215 yards) hit Ivan Huerta for six catches, 92 yards and a touchdown, while Diego Hernandez rushed for 110 yards on 19 carries.

“This is the consummate team sport, and everybody matters,” Franks said. “We had heard a lot about Manteca’s running game, and we felt like we have a running game also wanted to show that. Our offensive line got us going a little big, and Diego Hernandez had a good night. We got some good, tough, hard-fought yards in there.”