The bucket, the final for either side, cut the lead for No. 2-seeded Valle Vista League champion Covina (25-3) to a 37-19 advantage.
Overall, the Colts won the quarter, 11-3, in expanding a 26-16 halftime advantage.
"It was just one of those days when our shots weren't falling," said Spartans junior center Lauren Barsamian, who totaled eight points, eight rebounds and four steals. "We worked hard and even though we lost, we're still proud of each other."
Okazaki's three-pointer that closed the third was followed by a Colts 10-0 run in which Covina went up, 47-19, with 2:49 remaining after a pair of free throws from senior guard Ashli Baddorf.
Sophomore guard Courtney Chen scored La Cañada's other six points via a three-pointer and three free throws when she was fouled on a three-point attempt.
"Our defense is what fuels our team," said Covina Coach Nick Masi, who qualified his team to its first-ever quarterfinal berth. "We know that we're not the greatest offensively, so we have to play a lot of defense."
La Cañada's best quarter happened to be the first, in which the Spartans rallied from a quick 7-0 deficit with seven straight points, four of those coming from Barsamian and the other three off a triple from Chen.
Covina closed out the quarter with a 7-2 run interrupted only by a jumper from Sydney Zarate, set up by an assist from Mary Peck.
After the Colts jumped out to an 18-9 advantage in the second, La Cañada bounced back with a free throw from Barsamian followed by another three-pointer from Chen that pulled the Spartans within 18-13.
Yet, Covina finished the quarter with an 8-3 spurt to go up, 26-16, at halftime.
Chen led La Cañada with 12 points and two steals.
Baddorf paced the Colts with 16 points, while Elizabeth Velasquez added 12 points and Dominique Theus chipped in 11 points.
"This was sad, but we're really excited about next year," Barsamian said. "I don't think anyone expected us to go to the quarterfinals and we're looking forward to coming back next year."