La Cañada took a first-quarter lead and never gave it up, but the Titans (11-10, 4-4 in league) did make a charge in the fourth.
The nine-point lead, 27-18, the Spartans (14-10, 6-2) held with 55 seconds left in the third quarter was whittled down to five, 29-24, when San Marino's Kirstyn Leung (11 points, eight rebounds) hit a fadeaway jumper with 6:40 to go in the game.
The Titans were starting to take control and La Cañada's standout point guard Courtney Chen sensed the urgency.
The sophomore took the ball up the floor, pulled up and hit a three-pointer to give the Spartans a 34-25 lead with 4:30 remaining.
"I think that just picked our team up a lot and gave us some cushion, allowed us to take a deep breath and calm down," said Chen, who had a game-high 17 points.
La Cañada's Lauren Barsamian couldn't have been happier.
"I love when Courtney hits threes, she's my girl," said Barsamian, who finished with 12 points and a game-high 14 rebounds. "It felt great, I was going to get a rebound but I was glad I didn't have to."
San Marino kept it a two-possession game after a layup from Megan Coottauco (11 rebounds, four points and three steals) and two made free throws from Leung to cut the deficit to 34-29 with 2:43 left.
Chen stepped up again and worked her away past a full-court press and three Titans defenders and found Barsamian alone under the basket with a pretty pass for an easy bucket.
It was deja vu on La Cañada's next trip up the floor, as Chen found La Cañada's Sydney Zarate with a pass that led to a layup, foul and Zarate (seven points, 12 rebounds) cashing in the ensuing free throw to give the Spartans a 39-29 lead with 1:33 to go.
"[Chen] had a tremendous fourth quarter," Hill said. "Those two plays just put the game away."
San Marino started fouling in hopes of a dramatic comeback, but Chen sealed the deal by making five of her six free throws down the stretch as La Cañada held on for the win.
Fisher said his team may have felt some extra pressure on senior night, but he pushed the credit to the Spartans.
"I just think La Cañada beat us," he said. "They executed better and just took our offense away."