In 2010, when the Giants were on their way to a World Series victory, Barry Zito was rooting against them.

“I did,” Zito said recently. “It was really hard to admit.”

Zito makes the confession in his new memoir, “Curveball.” The book opens with manager Bruce Bochy telling Zito he was leaving him off the postseason roster — the biggest gut punch of his career.

“I rooted against the team because my ego was in full control and if we lost, then I could get out of there,” Zito said. “It would a) prove they couldn’t do it without me, and b) take me out of the situation because I was so miserable coming to the field every day.

“I was so deep in shame. I wanted out of that situation so bad.”

Not many athletes would make such a confession. But Zito bares his soul in his memoir. A man who seemingly always has been searching for answers thinks that he has some to share.

Now 41, Zito lives in Nashville with his wife, Amber, and their two sons. He has launched a music career, following in his parents’ footsteps, but took two years away from music to work on the book. “Curveball” is being released Tuesday by a Christian subsidiary of Harper Collins. Though some publishers were interested in Zito’s painfully honest tale, they backed off when they saw the Christian component.

“It actually comes in so late in the story, it’s not really a full Christian story,” Zito said. “I’ve been seeking truth my whole life, trying to find peace. I finally arrived at something and stopped looking.”

Zito tells his story, beginning with his parents. His father, Joe, was the product of a sexual assault by his grandfather on his stepdaughter, and because of that he was shamed as a child. When Joe had his own son, he overcompensated by convincing Barry he was the most talented, special kid around.

Zito’s mother, Roberta, grew up in a household dictated by her mother’s unconventional religious beliefs; his grandmother created the Society for the Teaching of the Inner Christ. Zito believes his exposure to such thinking created his need to search for inner peace and spirituality.

The end product was a searcher, a man who also believed he was better than everyone else.

“I felt superior to others because my parents always told me I was special,” he said, “but I was always looking for something else.”

Reporters used to be amused by Zito’s searching. As a young A’s pitcher, he traveled with his own pillow and stuffed animals. He read self-help books. He talked about controlling his mind. But we didn’t know how far he was willing to take it, or how desperately he needed validation. He took his father’s unrealistic expectations — 300 wins, 10 Cy Youngs — to heart.

His search got more intense after he signed his $126 million contract with the Giants and Brian Sabean, general manager at the time, told him, “You might as well tattoo that number on your forehead.” Why? Because that number would come to define him.

Zito hired a life coach. He smoked pot often, holed up in his $10 million house on top of Mount Tamalpais. He also had a lavish bachelor pad in the Hollywood Hills. He tried to connect with his spirit animal. He bought a 24-karat gold bar to be ingested. He dated famous actresses, thinking being on a red carpet would help his self-esteem.

“When I was growing up one person’s opinion defined me, and that was my father’s,” he said. “Then I transferred that to everyone else.”

When he was left off the 2010 roster, he called his father and said he was thinking about quitting baseball.

“Would you still love me, Dad?” he asked.

Zito didn’t quit the game. But he continued a destructive path. He destroyed his relationship with his close friend, former closer Brian Wilson.

“He became the most famous guy in baseball while my career was tanking, and I literally couldn’t handle it,” Zito said of the All-Star closer. “I pushed him away.”

Zito was miserable.

“Life became unmanageable,” he said. “I had to admit I was powerless over other people’s opinions.”

From the low point in 2010, there was nowhere to go but up. Zito married Amber Seyer after the 2011 season. She put a Bible in his hand. He started to find inner peace.

"Being humbled does amazing things," he said.

And then came the 2012 postseason, when Zito pitched an NLCS elimination game in St. Louis, shutting out the Cardinals for 7 ⅔ innings and sending the series back to San Francisco, where the Giants would win it. He followed that by pitching in Game 1 of the World Series, outdueling Detroit's Justin Verlander and giving up one earned run in 5 ⅔ innings in the win.

"I tried to get redemption for six years," he said. "When I finally let go of that need, I got what I had been trying to find."

We talked when Zito was in town to attend Buster and Kristen Posey's fundraiser for pediatric cancer at Oracle Park, where Zito played his guitar.

“Posey has always been an interesting character to me,” Zito said. “He was a golden child from the start. But he never gave any of that fame stuff any importance. He was so indifferent to it. He always had something else in his life, and baseball was not the end all and be all. You could see that every day in how he approached it.”

Zito wouldn’t trade his days with the Giants, even the miserable ones.

“I was a boy in Oakland,” he said, “but I became a man in San Francisco.”

Ann Killion is a San Francisco Chronicle columnist. Email: akillion@sfchronicle.com Twitter: @annkillion