St. Francis, which qualified for the playoffs last season for the second consecutive season under co-Coaches Jeff Stephens and Ray O'Brien, received 12 points and six rebounds from senior center Ian Hamilton and 10 from guard Ben Maynard.
The Golden Knights, who went 11-15 and 4-10 in the ultra-competitive Mission League last season before advancing to the second round of the CIF Southern Section Division 4-AA playoffs, led throughout Wednesday.
O'Brien said Gardea's basket changed the complexion of the contest.
"That play was big," O'Brien said. "Zack is a year older and he can get the ball in the basket.
"He's a streaky shooter. We have a lot of scorers because we bring a team that can shoot the ball well."
Junior forward Travis Talianko, a reigning member of the All-Area football team, grabbed an offensive rebound and scored on a layup to give the Golden Knights 25-19 lead with 22 seconds left in the first half.
St. Francis owned a 25-21 halftime advantage.
"Our coaches give us some leeway to be able to shoot jump shots," said Gardea, who made a three-pointer to give the Golden Knights a 14-6 lead with 6:41 remaining in the first quarter. "It's definitely one of our strengths.
"We are going to be playing in a lot of summer league games. It's going to give the players some more experience because we are sort of young."
St. Francis received nine points from junior guard Emerson Castaneda. Maynard scored seven second-half points for the Golden Knights.
"It's our first game of the summer and we are trying to determine a chemistry," said O'Brien, who lost starters Tommy Jordan, Justin Posthuma and Dietrich Riley to graduation. "A huge part of the beginning of summer will be to try to find chemistry to help us get better."