SANTA ANA >> Kevin Kiernan was surrounded by his cheering players before the water cooler emptied red and white confetti over his head. He was handed silver balloons that formed the number 900 and then watched a special tribute on the video board.

Mostly, Mater Dei’s longtime girls basketball coach was wrapped in love from his program and school Wednesday as he earned his 900th career victory as the No. 4-seeded Monarchs raced past No. 5 Mission Hills 71-47 in the first round of the CIF Southern California Open Division regional playoffs.

In the final home game of his 17-year tenure at Mater Dei, Kiernan reached the milestone to add to his state record for coaching girls basketball. His total of 900 wins includes his stops at La Quinta and Troy, and a combined collection of 12 CIF-SS titles, six state crowns and two national championships.

Earlier in the week, Kiernan, 64, announced that he will be stepping down after the playoffs because of health issues and the need for a “new voice” of Orange County’s powerhouse program. He will remain at the school as an athletic director.

While Kiernan said his departure has been in the works for some tine, he was caught off guard by the celebration in his honor Wednesday.

“That caught me big time by surprise,” said Kiernan, who also received a ball marked for his achievement. “I was shocked and obviously humbled. … (I felt) a lot gratitude. Sometimes you don’t realize the impact you make on people until they tell you.”

In advancing to Saturday’s semifinal at No. 1 Etiwanda, the Monarchs (25-7) were led by sophomore Kaeli Wynn and Duke-bound center Jenessa Cotton.

Wynn scored 24 of her 29 points in the second half, including three consecutive 3-pointers in the fourth. Cotton scored 15 of her 23 points in the first half and finished with 11 rebounds and two blocks.

Freshman point guard Chasity Rice came off the bench to record 14 points, seven rebounds and five assists. Junior guard Amaya Williams added eight rebounds and three steals.

Cotton said the Monarchs’ assistant coaches — Jesse Vargas, Pete Bonny, Alysa Ito, Brian Brennan and Jody Wynn — organized the surprise for Kiernan.

Kiernan’s fingerprints were already all over the victory. His trademark pressure defense — man-to-man and full-court press — limited the San Diego Section’s Open Division champion to five field goals and blocked three shots. Cotton reached behind a shooter for two of the blocks and Rice rejected a layup.

Kiernan hasn’t ruled out a comeback at some point. He added that he felt “conflicted” in his final home game.

“I’m pretty much at peace with my decision,” he said. “When you’ve coached for 40 years, you have your routines and (your year) goes by seasons. I’m always working over Christmas. Summer is summer league. Fall is fall league. I don’t know what I’m going to do when I don’t have to go to the gym to coach a game or come to practice. I’ll probably wander down here and watch.

“What do old retired coaches do? You hang around the gym.”

On Wednesday night, Kevin Kiernan felt loved as he hung around the gym a little longer than usual.